全文获取类型
收费全文 | 11351篇 |
免费 | 957篇 |
国内免费 | 69篇 |
专业分类
12377篇 |
出版年
2023年 | 90篇 |
2022年 | 124篇 |
2021年 | 251篇 |
2020年 | 208篇 |
2019年 | 236篇 |
2018年 | 349篇 |
2017年 | 338篇 |
2016年 | 409篇 |
2015年 | 545篇 |
2014年 | 524篇 |
2013年 | 823篇 |
2012年 | 967篇 |
2011年 | 940篇 |
2010年 | 575篇 |
2009年 | 489篇 |
2008年 | 741篇 |
2007年 | 648篇 |
2006年 | 603篇 |
2005年 | 660篇 |
2004年 | 649篇 |
2003年 | 523篇 |
2002年 | 367篇 |
2001年 | 120篇 |
2000年 | 100篇 |
1999年 | 70篇 |
1998年 | 61篇 |
1997年 | 58篇 |
1996年 | 49篇 |
1995年 | 48篇 |
1994年 | 49篇 |
1993年 | 52篇 |
1992年 | 41篇 |
1991年 | 36篇 |
1990年 | 41篇 |
1989年 | 40篇 |
1988年 | 28篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 39篇 |
1984年 | 45篇 |
1983年 | 34篇 |
1982年 | 44篇 |
1981年 | 30篇 |
1980年 | 26篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1976年 | 20篇 |
1975年 | 18篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
Mark I. Melhorn Abigail S. Brodsky Jessica Estanislau Joseph A. Khoory Ben Illigens Itaru Hamachi Yasutaka Kurishita Andrew D. Fraser Anne Nicholson-Weller Elena Dolmatova Heather S. Duffy Ionita C. Ghiran 《The Journal of biological chemistry》2013,288(43):31139-31153
Humans and other higher primates are unique among mammals in using complement receptor 1 (CR1, CD35) on red blood cells (RBC) to ligate complement-tagged inflammatory particles (immune complexes, apoptotic/necrotic debris, and microbes) in the circulation for quiet transport to the sinusoids of spleen and liver where resident macrophages remove the particles, but allow the RBC to return unharmed to the circulation. This process is called immune-adherence clearance. In this study we found using luminometric- and fluorescence-based methods that ligation of CR1 on human RBC promotes ATP release. Our data show that CR1-mediated ATP release does not depend on Ca2+ or enzymes previously shown to mediate an increase in membrane deformability promoted by CR1 ligation. Furthermore, ATP release following CR1 ligation increases the mobility of the lipid fraction of RBC membranes, which in turn facilitates CR1 clustering, and thereby enhances the binding avidity of complement-opsonized particles to the RBC CR1. Finally, we have found that RBC-derived ATP has a stimulatory effect on phagocytosis of immune-adherent immune complexes. 相似文献
82.
83.
During the last few years, geographical information systems (GIS) have spread as powerful tools for landscape analysis. The main purpose of this work was to use GIS to display an ecological network made up of core areas, key areas and ecological corridors. As an example of the application of this method we refer to the population of deer (Cervus elaphus) and roe deer (Capreolus capreolus) in an alpine area in northwestern Italy. The method provided an overall view of the ecological network of the area, highlighting how linear infrastructures can affect animal populations and consequently, their survival probability. 相似文献
84.
The essential oil obtained by hydrodistillation from the aerial parts of Tunisian endemic Hypericum triquetrifolium Turra (Clusiaceae) was analyzed using GC and GC-MS. One hundred and nine compounds consisting of 92.2% of total detected constituents were identified. Sesquiterpene hydrocarbons were the main constituents (59.37%), Alpha-humulene, cis-calamenene, delta-cadinene, bicyclogermacrene, eremophilene, betacaryophyllene and (E)-gamma-bisabolene were found as the main ones. Alpha-pinene (10.33%) was detected as the main monoterpene hydrocarbons (12.19%). The oxygenated sesquiterpenes constituted (9.33%); caryophyllene oxide (1.38%) was reported as the main constituent of this fraction. The oxygenated monoterpenes were weakly represented (4.62%) and consisted of constituents in low percentages (<1%). 相似文献
85.
Pascal Philibert Audrey Stoessel Wei Wang Annie-Paule Sibler Nicole Bec Christian Larroque Jeffery G Saven Jérôme Courtête Etienne Weiss Pierre Martineau 《BMC biotechnology》2007,7(1):81
Background
Intrabodies are defined as antibody molecules which are ectopically expressed inside the cell. Such intrabodies can be used to visualize or inhibit the targeted antigen in living cells. However, most antibody fragments cannot be used as intrabodies because they do not fold under the reducing conditions of the cell cytosol and nucleus. 相似文献86.
Raşit Urhan 《Biologia》2008,63(3):395-401
Two new species of zerconid mites, Zercon uludagicus sp. n. and Z. huseyini sp. n., from Turkey are described and illustrated. The similarities and differences between the species are discussed. The
lists of the taxonomic diagnostic key to adults of Zercon species known from Turkey are also given. 相似文献
87.
88.
Taxonomic confusion among closely related and morphologically similar Deprea species has persisted in the literature and in the identification of species. Morphological variation among three closely
related, monophyletic Deprea species was studied to determine if and how they can be distinguished. Their sympatric occurrence in Venezuela afforded an
opportunity to couple field study with analysis of herbarium specimens representing their entire geographic range. An analysis
of 94 morphological characters resulted in five vegetative and 13 reproductive taxonomically informative traits. Canonical
variates analysis clearly separated the three species using six quantitative traits. We conclude that these taxa, although
quite variable and similar morphologically, are taxonomically distinct. Results of character analysis indicated that D. orinocensis is morphologically more similar to D. bitteriana than either are to D. paneroi. In D. paneroi, small, sterile anthers on fruit-bearing plants and the absence of fruits on plants possessing large, plllen-bearing anthers,
suggest cryptic dioecy. Based on these data, D. granulosa is considered to be a synonym of D. orinocensis: Athenaea bitteriana, a misapplied synonym, is the correct basionym and is applicable to many specimens identified as D. granulosa. We submit a new combination, D. bitteriana (Werderm.) Sawyer & Benítez, and designate a lectotype to accommodate these findings. 相似文献
89.
Ghada Baraket Khaled Chatti Olfa Saddoud Ahmed Ben Abdelkarim Messaoud Mars Mokhtar Trifi Amel Salhi Hannachi 《Plant Molecular Biology Reporter》2011,29(1):171-184
This study characterises the genetic variability of fig, Ficus carica L., using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. It compares the efficiency
and utility of the two techniques in detecting variation and establishing genetic relationships among Tunisian fig cultivars.
Our results show that using both marker systems, the Tunisian fig germ plasm is characterised by having a large genetic diversity
at the deoxyribonucleic acid level, as most of AFLP bands were detected and all SSR markers were polymorphic. In fact, 351
(342 polymorphic) and 57 (57 polymorphic) bands were detected using AFLP and SSR primers, respectively. SSR markers were the
most polymorphic with an average polymorphic information content value of 0.94, while AFLP markers showed the highest effective
multiplex ratio (56.9) and marker index (45.2). The effective marker index was recorded highest (4.19) for AFLP markers and
lowest (0.70) for the SSR ones. Our results demonstrate that (1) independent as well as combined analyses of cluster analyses
of SSR and AFLP fragments showed that cultivars are clustered independently from their geographical origin, horticultural
classifications and tree sex; (2) the analysis of molecular variance allowed the partitioning of genetic variation within
and among fig groups and showed greater variation within groups and (3) AFLP and SSR markers datasets showed positive correlation.
This study suggests the SSR and AFLP markers are suitable for diversity analysis and cultivars fingerprinting. An understanding
of the genetic diversity and population structure of F. carica in Tunisia can also provide insight into the conservation and management of this species. 相似文献
90.
Fortuna?Ponte Gloria?MazzoneEmail authorView authors OrcID profile Nino?Russo Emilia?Sicilia 《Journal of molecular modeling》2018,24(7):183
Density functional theory and its time-dependent extension (DFT, TDDFT) were employed to establish the feasibility of using a series of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) in photodynamic therapy. Their absorption electronic spectra, singlet–triplet energy gaps, and spin–orbit matrix elements were computed and are discussed here. The effects of bromine substitution on the photophysical properties of BODIPY were elucidated. The investigated compounds were found to possess different excited triplet states that lie below the energy of the bright excited singlet state (S1 or S2), depending on the positions occupied by the bromine atoms. The computed spin–orbit matrix elements for the radiationless intersystem crossing Sn?→ ?Tm and the relative singlet–triplet energy gaps allowed the prediction of plausible nonradiative decay pathways for the production of singlet excited molecular oxygen, the key cytotoxic agent in photodynamic therapy. 相似文献