全文获取类型
收费全文 | 93257篇 |
免费 | 288篇 |
国内免费 | 901篇 |
专业分类
94446篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 22篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 11846篇 |
2017年 | 10674篇 |
2016年 | 7458篇 |
2015年 | 595篇 |
2014年 | 290篇 |
2013年 | 314篇 |
2012年 | 4230篇 |
2011年 | 12828篇 |
2010年 | 12011篇 |
2009年 | 8232篇 |
2008年 | 9784篇 |
2007年 | 11368篇 |
2006年 | 258篇 |
2005年 | 505篇 |
2004年 | 962篇 |
2003年 | 1014篇 |
2002年 | 773篇 |
2001年 | 255篇 |
2000年 | 159篇 |
1999年 | 28篇 |
1998年 | 8篇 |
1997年 | 24篇 |
1996年 | 10篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1993年 | 29篇 |
1992年 | 21篇 |
1991年 | 38篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 3篇 |
1984年 | 7篇 |
1983年 | 18篇 |
1982年 | 2篇 |
1975年 | 5篇 |
1972年 | 246篇 |
1971年 | 274篇 |
1970年 | 5篇 |
1965年 | 13篇 |
1962年 | 24篇 |
1956年 | 5篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Heather E. Wright Qiong Zhang James R. Mihelcic 《The International Journal of Life Cycle Assessment》2008,13(5):412-420
Goal, Scope, and Background The paper describes the integration of the economic input–output life cycle assessment (EIO-LCA) model and the environmental
fate and transport model (CHEMGL) with a risk assessment tool. Utilizing the EIO-LCA, instead of a traditional LCA, enables
a rapid, screening-level analysis of an emerging chemical of concern, decabromodiphenyl ether (DecaBDE). The risk assessment
in this study is evaluated based on the mass of chemical released, estimated concentrations, exposure, and chemical toxicity.
Methods The relative risk from ten economic sectors identified within the EIO-LCA model, 55 chemicals utilized in those sectors and
DecaBDE along with four potential DecaBDE breakdown products, were evaluated for the life cycle stages and exposure pathways.
The relative risk (expressed as toluene equivalents) of the different chemicals, sectors, and life cycle stages were compared
to assess those representing the greatest overall relative risks to humans (via inhalation and ingestion) and fish.
Results The greatest overall risk to human health resulted from the manufacturing and production stages. For fish, the manufacturing
stage represented virtually all of the risk. Of the 56 chemicals evaluated, DecaBDE represented the majority of the total
risk to humans. However, DecaBDE posed the least risk compared to its potential breakdown products.
Discussion The risk to humans from ingestion, which represented the greatest risk, from the production, manufacturing, and consumption
stages can be controlled and reduced through various safety precautions in the workplace. Additionally, the increasing concentration
of DecaBDE in anaerobic compartments represents a threat to humans and fish via the higher risk DecaBDE breakdown products.
Conclusions Overall, the manufacturing and production life cycle stages pose the greatest risk to humans and fish. The sediment compartment
received the highest DecaBDE concentration for the production, manufacturing, and consumption stages. This case study demonstrates
that the integrated EIO-LCA with risk assessment is suitable for screening-level analysis of emerging chemicals due to rapid
life cycle inventory analysis.
Recommendations The production and manufacturing stages allow for greater industry control and government regulation, compared to the consumption
stage, because there are fewer point sources. This integrated life cycle methodology may allow chemical designers to evaluate
each stage and assess areas where risks can be minimized. 相似文献
962.
Chin Woi Ho Wen Siang Tan Wei Boon Yap Tau Chuan Ling Beng Ti Tey 《Biotechnology and Bioprocess Engineering》2008,13(5):577-583
A comparative evaluation of five different cell-disruption methods for the release of recombinant hepatitis B core antigen
(HBcAg) from Escherichia coli was investigated. The cell disruption techniques evaluated in this study were high-pressure homogenization, batch-mode bead
milling, continuous-recycling bead milling, ultrasonication, and enzymatic lysis. Continuous-recycling bead milling was found
to be the most effective method in terms of operating cost and time. However, the highest degree of cell disruption and amounts
of HBcAg were obtained from the high-pressure homogenization process. The direct purification of HBcAg from the unclarified
cell disruptate derived from high-pressure homogenization and bead milling techniques, using batch anion-exchange adsorption
methods, showed that the conditions of cell disruption have a substantial effect on subsequent protein recovery steps. 相似文献
963.
Nguyen Van Du 《Kew Bulletin》2008,63(3):491-493
Summary
Typhonium stigmatilobatum V. D. Nguyen, a new species from Vietnam, is described and illustrated. 相似文献
964.
Jifeng Tang Samantha J Baldwin Jeanne ME Jacobs C Gerard van der Linden Roeland E Voorrips Jack AM Leunissen Herman van Eck Ben Vosman 《BMC bioinformatics》2008,9(1):374
Background
Simple Sequence Repeat (SSR) or microsatellite markers are valuable for genetic research. Experimental methods to develop SSR markers are laborious, time consuming and expensive. In silico approaches have become a practicable and relatively inexpensive alternative during the last decade, although testing putative SSR markers still is time consuming and expensive. In many species only a relatively small percentage of SSR markers turn out to be polymorphic. This is particularly true for markers derived from expressed sequence tags (ESTs). In EST databases a large redundancy of sequences is present, which may contain information on length-polymorphisms in the SSR they contain, and whether they have been derived from heterozygotes or from different genotypes. Up to now, although a number of programs have been developed to identify SSRs in EST sequences, no software can detect putatively polymorphic SSRs. 相似文献965.
Background
Lipocalins are a large and diverse family of small, mostly extracellular proteins implicated in many important functions. This family has been studied in bacteria, invertebrate and vertebrate animals but little is known about these proteins in plants. We recently reported the identification and molecular characterization of the first true lipocalins from plants, including the Apolipoprotein D ortholog AtTIL identified in the plant model Arabidopsis thaliana. This study aimed to determine its physiological role in planta. 相似文献966.
Yahya Al-Abed Emma Gray Konrad Wolfe Gavin W Watters Jonathan M Philpott 《International Seminars in Surgical Oncology : ISSO》2008,5(1):14
Background
Hurthle cell carcinoma of the thyroid is a rare form of thyroid cancer. It may present as a low grade tumour or can present as a more aggressive metastatic carcinoma. Hurthle cell carcinoma has the highest incidence of metastasis among all differentiated thyroid cancers. Most commonly haematogenous spread to lungs, bones and brain, however spread to regional lymph nodes is not uncommon. The breast is a rare site for metastasis from extramammary sources. We present the first case of breast metastasis from Hurthle cell carcinoma of the thyroid.Case presentation
We report a 77 year old lady who had total thyroidectomy and bilateral neck dissection followed by radiotherapy for a high grade metastatic Hurthle cell carcinoma of the thyroid. Ten months later she presented to the breast clinic with left breast lump and a lump at the left axilla. Fine needle aspiration cytology of the lumps and histology after wide local excision of the breast lump confirmed metastatic Hurthle cell carcinoma.Conclusion
The presence of breast lumps in patients with history of extramammary cancer should raise the possibility of metastasis.967.
Govind Ragupathi Payal Damani Geeta Srivastava Om Srivastava Steven J. Sucheck Yoshi Ichikawa Philip O. Livingston 《Cancer immunology, immunotherapy : CII》2009,58(9):1397-1405
Sialyl Lewisa (sLea), also termed CA19-9 antigen, is recognized by murine mAb19-9 and is expressed on the cancer cell surface as a glycolipid
and as an O-linked glycoprotein. It is highly expressed in a variety of gastrointestinal epithelial malignancies including
colon cancer and pancreatic cancer, and in breast cancer and small cell lung cancer, but has a limited expression on normal
tissues. sLea is known to be the ligand for endothelial cell selectins suggesting a role for sLea in cancer metastases and adhesion. For these reasons, sLea may be a good target for antibody mediated immunotherapy including monoclonal antibodies and tumor vaccines. However, sLea is structurally similar to sLex and other blood group related carbohydrates which are widely expressed on polymorphonucleocytes and other circulating cells,
raising concern that immunization against sLea will induce antibodies reactive with these more widely expressed autoantigens. We have shown previously both in mice and
in patients that conjugation of a variety of carbohydrate cancer antigen to keyhole limpet hemocyanin (KLH) and administration
of this conjugate mixed with saponin adjuvants QS-21 or GPI-0100 are the most effective methods for induction of antibodies
against these cancer antigens. We describe here for the first time the total synthesis of pentenyl glycoside of sLea hexasaccharide and its conjugation to KLH to construct a sLea-KLH conjugate. Groups of five mice were vaccinated subcutaneously four times over 6 weeks. Sera were tested against sLea-HSA by ELISA and against sLea positive human cell lines adenocarcinoma SW626 and small cell lung cancer (SCLC) DMS79 by FACS. As expected, mice immunized
with unconjugated sLea plus GPI-0100 or unconjugated sLea mixed with KLH plus GPI-0100 failed to produce antibodies against sLea. However, mice immunized with sLea-KLH conjugate without GPI-0100 produced low levels of antibodies and mice immunized with sLea-KLH plus GPI-0100 produced significantly higher titer IgG and IgM antibodies against sLea by ELISA. These antibodies were highly reactive by FACS and mediated potent complement mediated cytotoxicity against sLea positive SW626 and DMS79 cells. They showed no detectable cross reactivity against a series of other blood group-related
antigens, including Ley, Lex, and sLex by dot blot immune staining. This vaccine is ready for testing as an active immunotherapy for treating sLea positive cancer in clinical settings.
Govind Ragupathi and Philip O. Livingston are paid consultants and shareholders in MabVax Therapeutics, Inc., San Diego, CA
92121. The sLea vaccine is licensed to MabVax. 相似文献
968.
Numerous studies have revealed important functions for sialylation in both prokaryotes and higher animals. However, the genetic
and biochemical potential for sialylation in Drosophila has only been confirmed recently. Recent studies suggest significant similarities between the sialylation pathways of vertebrates
and insects and provide evidence for their common evolutionary origin. These new data support the hypothesis that sialylation
in insects is a specialized and developmentally regulated process which likely plays a prominent role in the nervous system.
Yet several key issues remain to be addressed in Drosophila, including the initiation of sialic acid de novo biosynthesis and understanding the structure and function of sialylated glycoconjugates. This review discusses our current
knowledge of the Drosophila sialylation pathway, as compared to the pathway in bacteria and vertebrates. We arrive at the conclusion that Drosophila is emerging as a useful model organism that is poised to shed new light on the function of sialylation not only in protostomes,
but also in a larger evolutionary context.
K. Koles and E. Repnikova contributed equally to this work. 相似文献
969.
The present work proposes new boundaries for the current submediterranean territories of the Iberian Peninsula, defining them
at the smallest scale attempted to date. The boundaries proposed are not sharp divisions but somewhat ‘gradual’, reflecting
the transitional nature of the territories they encompass. Climate change predictions were used to estimate how the distribution
of these submediterranean regions might change in the near future. The maps constructed are based on the distribution of marcescent
Quercus species—trees that characterise the submediterranean plant landscape where they form the main forest communities. To determine
their climatic range, the distribution of different types of Iberian oak forest was represented in ‘climate diagrams’ (ordination
diagrams derived from principal components analysis), both in terms of individual species and groups of species based on leaf
ecophysiological type, i.e. marcescent (Submediterranean), sclerophyllous (Mediterranean), semideciduous (Mediterranean) and
deciduous (Eurosiberian). The climate range of each type of forest was determined, and the means of representative climate
variables are analysed by one way ANOVA. The variables differentiating the forest groups were also examined by discriminant
analysis. The range of the climate variables found to be associated with the majority of marcescent forests was used to determine
the distribution of territories throughout the Peninsula with the same conditions (i.e. whether marcescent forests were present
or not), thus providing a map of the Iberian submediterranean territories. Predictions of climate change were used to investigate
possible climate-induced modifications in the boundaries of these territories in the near future. The patterns obtained show
dramatic reductions in the extension of the Iberian submediterranean environment. Submediterranean conditions will probably
disappear from the areas where they currently reign, and it seems unlikely that any new, large submediterranean areas will
form by displacement towards higher altitudes. The outlook for the unique submediterranean vegetation of the Iberian Peninsula
is gloomy.
相似文献
Helios Sainz-OlleroEmail: |
970.
Yoshiaki Tsuda Madoka Kimura Shuri Kato Toshio Katsuki Yuzuru Mukai Yoshihiko Tsumura 《Journal of plant research》2009,122(4):367-375
The genetic resources of a particular species of flowering cherry, Cerasus jamasakura, have high conservation priority because of its cultural, ecological and economic value in Japan. Therefore, the genetic
structures of 12 natural populations of C. jamasakura were assessed using ten nuclear SSR loci. The population differentiation was relatively low (F
ST, 0.043), reflecting long-distance dispersal of seeds by animals and historical human activities. However, a neighbor-joining
tree derived from the acquired data, spatial analysis of molecular variance and STRUCTURE analysis revealed that the populations
could be divided into two groups: one located on Kyusyu Island and one on Honshu Island. Genetic diversity parameters such
as allelic richness and gene diversity were significantly lower in the Kyushu group than the Honshu group. Furthermore, STRUCTURE
analysis revealed that the two lineages were admixed in the western part of Honshu Island. Thus, although the phylogeographical
structure of the species and hybridization dynamics among related species need to be evaluated in detail using several marker
systems, the Kyusyu Island and Honshu Island populations should be considered as different conservation units, and the islands
should be regarded as distinct seed transfer zones for C. jamasakura, especially when rapid assessments are required. 相似文献