全文获取类型
收费全文 | 2503篇 |
免费 | 357篇 |
出版年
2021年 | 26篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 33篇 |
2017年 | 31篇 |
2016年 | 54篇 |
2015年 | 66篇 |
2014年 | 78篇 |
2013年 | 93篇 |
2012年 | 128篇 |
2011年 | 129篇 |
2010年 | 82篇 |
2009年 | 71篇 |
2008年 | 108篇 |
2007年 | 85篇 |
2006年 | 77篇 |
2005年 | 77篇 |
2004年 | 78篇 |
2003年 | 69篇 |
2002年 | 76篇 |
2001年 | 104篇 |
2000年 | 108篇 |
1999年 | 84篇 |
1998年 | 53篇 |
1997年 | 46篇 |
1996年 | 65篇 |
1995年 | 44篇 |
1994年 | 48篇 |
1993年 | 27篇 |
1992年 | 77篇 |
1991年 | 63篇 |
1990年 | 56篇 |
1989年 | 52篇 |
1988年 | 53篇 |
1987年 | 32篇 |
1986年 | 35篇 |
1985年 | 45篇 |
1984年 | 36篇 |
1983年 | 28篇 |
1982年 | 19篇 |
1980年 | 20篇 |
1979年 | 27篇 |
1978年 | 21篇 |
1977年 | 34篇 |
1973年 | 16篇 |
1972年 | 25篇 |
1971年 | 20篇 |
1969年 | 18篇 |
1967年 | 14篇 |
1966年 | 16篇 |
排序方式: 共有2860条查询结果,搜索用时 15 毫秒
111.
Russell B. Lingham Keith C. Silverman Gerald F. Bills Carmen Cascales Manual Sanchez Rosalind G. Jenkins Suzanne E. Gartner Isabel Martin Maria T. Diez Fernando Peláez Sagrario Mochales Yu-Lin Kong Richard W. Burg Maria S. Meinz Leeyuan Huang Mary Nallin-Omstead Scott D. Mosser Michael D. Schaber Charles A. Omer David L. Pompliano Jackson B. Gibbs Sheo B. Singh 《Applied microbiology and biotechnology》1993,40(2-3):370-374
Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella.
Correspondence to: R. B. Lingham 相似文献
112.
Submaximal,aerobic exercise training exacerbates the cardiomyopathy of postweanling Cu-depleted rats
Jeannette Davidson Denis M. Medeiros Robert L. Hamlin James E. Jenkins 《Biological trace element research》1993,38(3):251-272
To determine the dual effect of exercise training and copper depletion on myocardial function and ultrastructure, postweanling
rats were either trained or sedentary while fed copper-adequate or copper-deficient diets for 8 wk. Rats developed characteristic
myocardial subcellular degeneration and increased cardiac mitochondrial volume density when copper depleted, despite lack
of overt cardiac hypertrophy, hypertension, or anemia. Training combined with copper depletion induced mild left ventricular
hypertrophy. Basal laminae appeared fractionated in areas at capillary-myocyte interface, with focal pericapillary and interstitial
collagen accumulation, where-as overt fibrosis was absent or minimal. Electrocardiograms revealed increased QRS wave and QT
duration and notching of QRS complex with copper depletion, consistent with intraventricular conductance disturbances. The
oxidative capacity of soleus muscle increased with training in copper-adequate rats, but was reduced with progressive copper
depletion. These data suggest that copper depletion and training are synergistic in effecting focal accumulation of collagen,
with deleterious effect on exercise capacity. 相似文献
113.
Louis Faso Richard S. Trowbridge Wei Quan Xiu-Lan Yao Edmund C. Jenkins Alma Maciulis Thomas D. Bunch Henry M. Wisniewski 《In vitro cellular & developmental biology. Animal》1994,30(4):226-235
Summary A strain of cerebral endothelial cells was established from isolated cortical microvessels of caprine brain. These cells,
which are referred to as ECl cells, can be routinely subcultured to 32 passages without the loss of differentiated morphologic
and immunologic traits. The ability to routinely subculture ECl cells is an important asset, given that isolated cerebral
endothelial cells in mammals generally lose their differentiated traits after only 2 to 3 passages.
ECl cells were shown to contain Factor VIII-related antigen, which is a specific marker for cells of endothelial origin. ECl
cells morphologically demonstrated a scarcity of pinocytotic vesicles on their apical surfaces, a lack of trans-cytoplasmic
vesicles, and the ability to form in culture confluent monolayers with tight junctional complexes. Therefore, ECl cells possess
specific antigenic and ultrastructural features which classify them as being small vessel endothelial cells of the blood-brain
barrier type. Cytogenetic evaluation of ECl cells demonstrated a normal female goat 60,XX karyotype and confirmed the apparent
non-transformed nature of ECl cells due to the lack of chromosome abnormalities or rearrangements. Using scanning electron
microscopy, ECl cells were also shown to form confluent monolayers on mixed nitrocellulose filters, a feature that will enable
the development of an in vitro system to study trans-endothelial transport. Given that ECl cells are readily subcultured and
grow well on nitrocellulose filters, and that they resemble cerebral endothelium in vivo, it seems evident that ECl cells
can be used as a versatile model for the study of blood-brain barrier function, regulation, and pathology. 相似文献
114.
Rowan Jenkins 《The Botanical review》1993,59(2):81-111
A review of methods used in the taxonomy of the Fagaceae is presented, with a critical focus made on the nomenclature of extant and fossil taxa, notablyNothofagus. The most recent classifications of the family and the problems of character weighting are considered, and an argument is made to reduce the subfamilies to tribes. The origin of the cupule is then discussed. Interpretations of the cupule as a series of reduced dichasial axes are criticized for their essentialistic approach, lack of evolutionary evidence and failure of application to the family as a whole. With the postulating of an ancestral form, the origin of the cupule involving a combination of characters from an outer tripartite perianth whorl and the pericarp is proposed. The theory provides for the evolution of the thin-walled dry pericarp and all the cupule forms found in the family today. 相似文献
115.
116.
Sinlan Poo Ana Karen Candia Kristina L. Cohen Francesca T. Erickson Sara A. Mason Bradley D. Nissen Adair F. McNear Jonathon J. Reinig Joseph S. Sherrock Ashley R. Aguiluz Letitia L. Jacques Hanna E. R. Jenkins Anne Devan-Song 《Biotropica》2023,55(4):806-815
Environmentally cued hatching has been well-documented in amphibians in response to a wide range of abiotic and biotic factors. The hatching of terrestrial amphibian eggs in response to flooding may be basal within the group, but amphibian lineages in tropical Asia and sub-Saharan Africa have not received as much attention as their Neotropical counterparts. We investigated submergence-induced hatching in Feihyla hansenae, a Rhacophorid tree frog with terrestrial eggs. We quantified natural rates of clutch submergence at our study site in Thailand. Using submergence experiments, we found that embryos are capable of hatching early to escape flooding, and that failure to hatch results in mortality. Among the embryos that were able to hatch early, only the earliest, youngest hatchlings experienced a trade-off in body size that persisted for 6 days, while later, older hatchlings were not significantly smaller than spontaneous hatchlings under control conditions. By incorporating our natural and experimental data into Monte Carlo methods to simulate and compare survival probabilities with and without hatching plasticity, we found an overall 3.1% increase in submergence survival due to hatching plasticity. Our findings support the idea that flooding-induced hatching is widespread across amphibians with terrestrial eggs and highlight the importance of researching understudied tropical regions. As climate change is projected to affect rainfall patterns, the ability of embryos to escape abiotic egg-stage threats may be an indicator of species' ability to flexibly navigate a changing environment. 相似文献
117.
Kristofer M. Gomes Brook L. Nunn P. Dreux Chappell Bethany D. Jenkins 《Journal of phycology》2023,59(5):1085-1099
Diatoms are important primary producers in the world's oceans, yet their growth is constrained in large regions by low bioavailable iron (Fe). Low-Fe stress-induced limitation of primary production is due to requirements for Fe in components of essential metabolic pathways including photosynthesis and other chloroplast plastid functions. Studies have shown that under low-Fe stress, diatoms alter plastid-specific processes, including components of electron transport. These physiological changes suggest changes of protein content and in protein abundances within the diatom plastid. While in silico predictions provide putative information on plastid-localized proteins, knowledge of diatom plastid proteins remains limited in comparison to well-studied model photosynthetic organisms. To address this, we employed shotgun proteomics to investigate the proteome of subcellular plastid-enriched fractions from Thalassiosira pseudonana to gain a better understanding of how the plastid proteome is remodeled in response to Fe limitation. Using mass spectrometry-based peptide identification and quantification, we analyzed T. pseudonana grown under Fe-replete and -limiting conditions. Through these analyses, we inferred the relative quantities of each protein, revealing that Fe limitation regulates major metabolic pathways in the plastid, including the Calvin cycle. Additionally, we observed changes in the expression of light-harvesting proteins. In silico localization predictions of proteins identified in this plastid-enriched proteome allowed for an in-depth comparison of theoretical versus observed plastid-localization, providing evidence for the potential of additional protein import pathways into the diatom plastid. 相似文献
118.
Florence W. L. Tsui Hing-Wo Tsui Samuel Mok Irena Mlinaric Neal G. Copeland Debra J. Gilbert Nancy A. Jenkins Katherine A. Siminovitch 《Genomics》1993,15(3)
Stefins or Type 1 cystatins belong to a large, evolutionarily conserved protein superfamily, the members of which inhibit the papain-like cysteine proteinases. We report here on the molecular cloning and chromosomal localization of three newly identified members of the murine stefin gene family. These genes, designated herein as mouse stefins 1, 2, and 3, were isolated on the basis of their relatively increased expression in moth-eaten viable compared to normal congenic mouse bone marrow cells. The open reading frames of the stefin cDNAs encode proteins of approximately 11.5 kDa that show between 50 and 92% identity to sequences of stefins isolated from various other species. Data from Southern analysis suggest that the murine stefin gene family encompasses at least 6 and possibly 10-20 members, all of which appear to be clustered in the genome. Analysis of interspecific backcross mice indicates that the genes encoding the three mouse stefins all map to mouse chromosome 16, a localization that is consistent with the recent assignment of the human stefin A gene to a region of conserved homology between human chromosome 3q and the proximal region of mouse chromosome 16. 相似文献
119.
Significance of betaines in the increased chlorophyll content of plants treated with seaweed extract 总被引:2,自引:0,他引:2
Seaweed extract, prepared by alkaline extraction of Ascophyllum nodosum (L.) Le Jol., applied either to the soil or to the foliage of tomato plants, produced leaves with higher chlorophyll levels
than those of control plants. The effects on leaf chlorophyll content were investigated using a cucumber bioassay procedure
devised for cytokinins. The seaweed extract was shown to increase the chlorophyll levels of the cucumber cotyledons, but ‘peaks’
of activity were obtained when widely different concentrations were used. The possibility that these effects were the result
of betaines present in the extract was considered. Glycinebetaine, γ-aminobutyric acid betaine and δ-aminovaleric acid betaine
all produced significantly enhanced chlorophyll concentrations in the cotyledons. ‘Peaks’ of activity were observed for each
betaine: for glycinebetaine at 10−6 and between 10−4 and 101 mg 1−1, for γ-aminobutyric acid betaine at 10−6, between 10−4 and 10−1, and 101 mg 1−1, and for δ-aminovaleric acid betaine between 10−5 and 101 mg 1−1. It was concluded that the effects of enhancing chlorophyll levels produced by the seaweed extract were due, at least in
part, to betaines. 相似文献
120.
J. O. Caldecott M. D. Jenkins T. H. Johnson B. Groombridge 《Biodiversity and Conservation》1996,5(6):699-727
The Convention on Biological Diversity aims to encourage and enable countries to conserve biological diversity, to use its components sustainably and to share benefits equitably. Species richness and endemism are two key attributes of biodiversity that reflect the complexity and uniqueness of natural ecosystems. National data on vertebrates and higher plants indicate global concentrations of biodiversity and can assist in defining priorities for action. Projections indicate that species and ecosystems will be at maximum risk from human activities during the next few decades. Prompt action by the world community can minimise the eventual loss of species. Highest priorities should be to: (i) strengthen the management of ecosystems containing a large proportion of global biodiversity; (ii) help developing countries complete their biodiversity strategies and action plans, monitor their own biodiversity, and establish and maintain adequate national systems of conservation areas; (iii) support actions at the global level, providing benefit to all countries in managing their own biodiversity. Generally, resources will best be spent in safeguarding ecosystems and habitats that are viable and important for global biodiversity, and which are threatened by factors that can be controlled cost-effectively. Other important criteria are representativeness, complementarity and insurance. 相似文献