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991.
Diana Stralberg D. Richard Cameron Mark D. Reynolds Catherine M. Hickey Kirk Klausmeyer Sylvia M. Busby Lynne E. Stenzel W. David Shuford Gary W. Page 《Biodiversity and Conservation》2011,20(1):19-40
Conservation of migratory shorebirds and waterfowl presents unique challenges due to extensive historic loss of wetland habitats, and current reliance on managed landscapes for wintering and migratory passage. We developed a spatially-explicit approach to estimate potential shorebird and waterfowl densities in California by integrating mapped habitat layers and statewide bird survey data with expert-based habitat rankings. Using these density estimates as inputs, we used the Marxan site-selection program to identify priority shorebird and waterfowl areas at the ecoregional level. We identified 3.7 million ha of habitat for shorebirds and waterfowl, of which 1.4 million ha would be required to conserve 50% of wintering populations. To achieve a conservation goal of 75%, more than twice as much habitat (3.1 million ha) would be necessary. Agricultural habitats comprised a substantial portion of priority areas, especially at the 75% level, suggesting that under current management conditions, large areas of agricultural land, much of it formerly wetland, are needed to provide the habitat availability and landscape connectivity required by shorebird and waterfowl populations. These habitats were found to be largely lacking recognized conservation status in California (96% un-conserved), with only slightly higher levels of conservation for priority shorebird and waterfowl areas. Freshwater habitats, including wetlands and ponds, were also found to have low levels of conservation (67% un-conserved), although priority shorebird and waterfowl areas had somewhat higher levels of conservation than the state as a whole. Conserving migratory waterfowl and shorebirds will require a diversity of conservation strategies executed at a variety of scales. Our modeled results are complementary with other approaches and can help prioritize areas for protection, restoration and other actions. Traditional habitat protection strategies such as conservation easements and fee acquisitions may be of limited utility for protecting and managing significant areas of agricultural lands. Instead, conservation strategies focused on incentive-based programs to support wildlife friendly management practices in agricultural settings may have greater utility and conservation effectiveness. 相似文献
992.
993.
Aloke K. Bera Nancy W. Y. Ho Aftab Khan Miroslav Sedlak 《Journal of industrial microbiology & biotechnology》2011,38(5):617-626
Robust microorganisms are necessary for economical bioethanol production. However, such organisms must be able to effectively
ferment both hexose and pentose sugars present in lignocellulosic hydrolysate to ethanol. Wild type Saccharomyces cerevisiae can rapidly ferment hexose, but cannot ferment pentose sugars. Considerable efforts were made to genetically engineer S. cerevisiae to ferment xylose. Our genetically engineered S cerevisiae yeast, 424A(LNH-ST), expresses NADPH/NADH xylose reductase (XR) that prefer NADPH and NAD+-dependent xylitol dehydrogenase (XD) from Pichia stipitis, and overexpresses endogenous xylulokinase (XK). This strain is able to ferment glucose and xylose, as well as other hexose
sugars, to ethanol. However, the preference for different cofactors by XR and XD might lead to redox imbalance, xylitol excretion,
and thus might reduce ethanol yield and productivity. In the present study, genes responsible for the conversion of xylose
to xylulose with different cofactor specificity (1) XR from N. crassa (NADPH-dependent) and C. parapsilosis (NADH-dependent), and (2) mutant XD from P. stipitis (containing three mutations D207A/I208R/F209S) were overexpressed in wild type yeast. To increase the NADPH pool, the fungal
GAPDH enzyme from Kluyveromyces lactis was overexpressed in the 424A(LNH-ST) strain. Four pentose phosphate pathway (PPP) genes, TKL1, TAL1, RKI1 and RPE1 from S. cerevisiae, were also overexpressed in 424A(LNH-ST). Overexpression of GAPDH lowered xylitol production by more than 40%. However, other
strains carrying different combinations of XR and XD, as well as new strains containing the overexpressed PPP genes, did not
yield any significant improvement in xylose fermentation. 相似文献
994.
Ding Haixia Zhang Jingsong Jiang Lei Dong Hairong Wang Jun Xiao Hang Chen Weixian 《Cell biochemistry and biophysics》2011,59(1):39-47
Extracellular domains of the transmembrane glycoprotein, neuropilin-1 (Np1), specifically bind an array of factors and co-receptors
including class-3 semaphorins (Sema3a), vascular endothelial growth factor (VEGF), hepatocyte growth factor, platelet-derived
growth factor BB, transforming growth factor-β 1 (TGF-β1), and fibroblast growth factor2 (FGF2). Np1 may have a role in immune
response, tumor cell growth, and angiogenesis, but its relative expression in comparison to its co-primary receptors, VEGF
and Sema3a, is not known. In this study we determined the mRNA expression of Np1 and its co-receptors, VEGF and Sema3a, and
the ratio of VEGF/Sema3a in different human and rodent cell lines. Expression of Np1, VEGF and Sema3a is very low in cells
derived from normal tissues, but these proteins are highly expressed in tumor-derived cells. Furthermore, the ratio of VEGF/Sema3a
is highly variable in different tumor cells. The elevated mRNA expression of Np1 and its putative receptors in tumor cells
suggests a role for these proteins in tumor cell migration and angiogenesis. As different tumor cells exhibit varying VEGF/Sema3a
ratios, it appears that cancer cells show differential response to angiogenic factors. These results bring to light the individual
variation among the cancer-related genes, Np1, VEGF, and Sema3a, and provide an important impetus for the possible personalized
therapeutic approaches for cancer patients. 相似文献
995.
Mai Kanke Kohei Nishimura Masato Kanemaki Tatsuo Kakimoto Tatsuro S Takahashi Takuro Nakagawa Hisao Masukata 《BMC cell biology》2011,12(1):8
Background
Inducible inactivation of a protein is a powerful approach for analysis of its function within cells. Fission yeast is a useful model for studying the fundamental mechanisms such as chromosome maintenance and cell cycle. However, previously published strategies for protein-depletion are successful only for some proteins in some specific conditions and still do not achieve efficient depletion to cause acute phenotypes such as immediate cell cycle arrest. The aim of this work was to construct a useful and powerful protein-depletion system in Shizosaccaromyces pombe. 相似文献996.
Paul W. Weber Laurens E. Howle Mark M. Murray Joseph M. Corless 《Biophysical journal》2011,100(3):525
When radiolabeled precursors and autoradiography are used to investigate turnover of protein components in photoreceptive cone outer segments (COSs), the labeled components—primarily visual pigment molecules (opsins)—are diffusely distributed along the COS. To further assess this COS labeling pattern, we derive a simplified mass-transfer model for quantifying the contributions of advective and diffusive mechanisms to the distribution of opsins within COSs of the frog retina. Two opsin-containing regions of the COS are evaluated: the core axial array of disks and the plasmalemma. Numerical solutions of the mass-transfer model indicate three distinct stages of system evolution. In the first stage, plasmalemma diffusion is dominant. In the second stage, the plasmalemma density reaches a metastable state and transfer between the plasmalemma and disk region occurs, which is followed by an increase in density that is qualitatively similar for both regions. The final stage consists of both regions slowly evolving to the steady-state solution. Our results indicate that autoradiographic and cognate approaches for tracking labeled opsins in the COS cannot be effective methodologies for assessing new disk formation at the base of the COS. 相似文献
997.
Strecker AL Casselman JM Fortin MJ Jackson DA Ridgway MS Abrams PA Shuter BJ 《Oecologia》2011,166(3):819-831
Species present in communities are affected by the prevailing environmental conditions, and the traits that these species
display may be sensitive indicators of community responses to environmental change. However, interpretation of community responses
may be confounded by environmental variation at different spatial scales. Using a hierarchical approach, we assessed the spatial
and temporal variation of traits in coastal fish communities in Lake Huron over a 5-year time period (2001–2005) in response
to biotic and abiotic environmental factors. The association of environmental and spatial variables with trophic, life-history,
and thermal traits at two spatial scales (regional basin-scale, local site-scale) was quantified using multivariate statistics
and variation partitioning. We defined these two scales (regional, local) on which to measure variation and then applied this
measurement framework identically in all 5 study years. With this framework, we found that there was no change in the spatial
scales of fish community traits over the course of the study, although there were small inter-annual shifts in the importance
of regional basin- and local site-scale variables in determining community trait composition (e.g., life-history, trophic,
and thermal). The overriding effects of regional-scale variables may be related to inter-annual variation in average summer
temperature. Additionally, drivers of fish community traits were highly variable among study years, with some years dominated
by environmental variation and others dominated by spatially structured variation. The influence of spatial factors on trait
composition was dynamic, which suggests that spatial patterns in fish communities over large landscapes are transient. Air
temperature and vegetation were significant variables in most years, underscoring the importance of future climate change
and shoreline development as drivers of fish community structure. Overall, a trait-based hierarchical framework may be a useful
conservation tool, as it highlights the multi-scaled interactive effect of variables over a large landscape. 相似文献
998.
High salinity is an environmental factor that inhibits plant growth and development, leading to large losses in crop yields.
We report here that mutations in SIZ1 or PHO2, which cause more accumulation of phosphate compared with the wild type, enhance tolerance to salt stress. The siz1 and pho2 mutations reduce the uptake and accumulation of Na+. These mutations are also able to suppress the Na+ hypersensitivity of the sos3-1 mutant, and genetic analyses suggest that SIZ1 and SOS3 or PHO2 and SOS3 have an additive effect on the response to salt stress. Furthermore, the siz1 mutation cannot suppress the Li+ hypersensitivity of the sos3-1 mutant. These results indicate that the phosphate-accumulating mutants siz1 and pho2 reduce the uptake and accumulation of Na+, leading to enhanced salt tolerance, and that, genetically, SIZ1 and PHO2 are likely independent of SOS3-dependent salt signaling. 相似文献
999.
Phloem loading is the process by which photoassimilates synthesized in the mesophyll cells of leaves enter the sieve elements
and companion cells of minor veins in preparation for long distance transport to sink organs. Three loading strategies have
been described: active loading from the apoplast, passive loading via the symplast, and passive symplastic transfer followed
by polymer trapping of raffinose and stachyose. We studied phloem loading in Amborella trichopoda, a premontane shrub that may be sister to all other flowering plants. The minor veins of A. trichopoda contain intermediary cells, indicative of the polymer trap mechanism, forming an arc on the abaxial side and subtending a
cluster of ordinary companion cells in the interior of the veins. Intermediary cells are linked to bundle sheath cells by
highly abundant plasmodesmata whereas ordinary companion cells have few plasmodesmata, characteristic of phloem that loads
from the apoplast. Intermediary cells, ordinary companion cells, and sieve elements form symplastically connected complexes.
Leaves provided with 14CO2 translocate radiolabeled sucrose, raffinose, and stachyose. Therefore, structural and physiological evidence suggests that
both apoplastic and polymer trapping mechanisms of phloem loading operate in A. trichopoda. The evolution of phloem loading strategies is complex and may be difficult to resolve. 相似文献
1000.
Basu A 《Statistics in biosciences》2011,3(1):6-27
Instrumental variables methods (IV) are widely used in the health economics literature to adjust for hidden selection biases
in observational studies when estimating treatment effects. Less attention has been paid in the applied literature to the
proper use of IVs if treatment effects are heterogeneous across subjects. Such a heterogeneity in effects becomes an issue
for IV estimators when individuals’ self-selected choices of treatments are correlated with expected idiosyncratic gains or
losses from treatments. We present an overview of the challenges that arise with IV estimators in the presence of effect heterogeneity
and self-selection and compare conventional IV analysis with alternative approaches that use IVs to directly address these
challenges. Using a Medicare sample of clinically localized breast cancer patients, we study the impact of breast-conserving
surgery and radiation with mastectomy on 3-year survival rates. Our results reveal the traditional IV results may have masked
important heterogeneity in treatment effects. In the context of these results, we discuss the advantages and limitations of
conventional and alternative IV methods in estimating mean treatment-effect parameters, the role of heterogeneity in comparative
effectiveness research and the implications for diffusion of technology. 相似文献