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991.
992.
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
993.
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
994.
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995.
我国西南部喀斯特森林特有濒危树种掌叶木新的微卫星分子标记的开发 总被引:1,自引:0,他引:1
采用基因组DNA富集文库法FIASCO(Fast isolation by AFLP of sequences containing repeats)从掌叶木(Handeliodendron bodinieri)基因组中分离和筛选了10个新的微卫星位点,进而对掌叶木茂兰自然分布居群的遗传多样性进行了分析。结果表明, 每个位点在30株掌叶木个体上的平均等位基因数(A)为3.5(3~5个),平均观察杂合度(HO)为0.650(0.267~0.900),平均预期杂合度(HE)为0.494(0.224~0.652)。每个位点的第一排除概率值Pr(Ex1)为0.029~0.240,位点综合值为0.7496。单个位点的第二排除概率Pr(Ex2)为0.123~0.419,位点综合值为0.9517。这些信息预示着这些微卫星标记可以为研究喀斯特特有濒危树种掌叶木的基因流及居群遗传结构提供有效的遗传工具。 相似文献
996.
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
997.
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
998.
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
999.
Yifeng Miao Yongming Qiu Yuchang Lin Zengli Miao Jing Zhang Xiaojie Lu 《Molecular biology reports》2011,38(5):3235-3242
Pyruvate, an endogenous metabolite of glycolysis, is an anti-toxicity agent. Recent studies have suggested possible roles
for pyruvate in protecting CNS neurons from excitotoxic and metabolic insults. Utilizing cultures derived from embryonic rat
cortex, the studies presented in this paper indicate that an astroglia-mediated mechanism is involved in the neuroprotective
effects of pyruvate against glutamate toxicity. Glutamate-induced toxicity could be reversed by pyruvate in a mixed culture
of cortex cells. Importantly, in pure neuronal cultures from the same tissue, pyruvate failed to protect against glutamate
toxicity. Addition of astroglia to the pure neuronal cultures restores the ability of pyruvate to protect neurons from glutamate-induced
toxicity. Our results further suggest that pyruvate can induce glia to up-regulate the synthesis of glutathione (GSH), an
antioxidant that protects cells from toxins such as free radicals. Taken together, our data suggest that astroglia in mixed
cultures are essential for mediating the effects of pyruvate, revealing a novel mechanism by which pyruvate, an important
intermediate of tricarboxylic acid cycle in the body, may act to protect neurons from damage during insults such as brain
ischemia. 相似文献
1000.
To determine the species of the yeast-like symbionts (YLS) in the brown planthoppers (BPH), Nilaparvata lugens, YLS were first isolated and purified by ultracentrifugation from the fat bodies of BPH, and then 18S rDNA and internal transcribed
spacer (ITS)–5.8S rDNA sequences of YLS were amplified with the different general primers for fungi. The results showed that
the two different 18S and ITS–5.8S rDNA sequences of YLS were obtained. One 2291-bp DNA sequence, which contained 18S and
ITS–5.8S rDNA, showed the high similarity to Cryptococcus and was named Cryp-Like symbiotes. Another 1248-bp DNA sequence, which contained a part of 18S and ITS–5.8S rDNA, showed the high similarity
to Pichia guilliermondii and was named Pichia-Like symbiotes. It was further proved that Cryp- and Pichia-Like symbiotes existed in BPH through nested PCR with specific primers for two symbiotes and in situ hybridization analysis
using digoxigenin-labeled probes. Our results showed that BPH harbored more than one species of eukaryotic YLS, which suggested
that diversity of fungal endosymbiotes may be occurred in planthoppers, just like bacterial endosymbiotes. 相似文献