全文获取类型
收费全文 | 62455篇 |
免费 | 4467篇 |
国内免费 | 3349篇 |
出版年
2024年 | 77篇 |
2023年 | 738篇 |
2022年 | 1285篇 |
2021年 | 1475篇 |
2020年 | 1385篇 |
2019年 | 1802篇 |
2018年 | 1809篇 |
2017年 | 1330篇 |
2016年 | 1499篇 |
2015年 | 2088篇 |
2014年 | 3081篇 |
2013年 | 4283篇 |
2012年 | 2251篇 |
2011年 | 3164篇 |
2010年 | 2553篇 |
2009年 | 3223篇 |
2008年 | 3469篇 |
2007年 | 3470篇 |
2006年 | 3222篇 |
2005年 | 3143篇 |
2004年 | 2815篇 |
2003年 | 2502篇 |
2002年 | 2332篇 |
2001年 | 1516篇 |
2000年 | 1295篇 |
1999年 | 1414篇 |
1998年 | 1431篇 |
1997年 | 1207篇 |
1996年 | 964篇 |
1995年 | 1093篇 |
1994年 | 1016篇 |
1993年 | 889篇 |
1992年 | 804篇 |
1991年 | 584篇 |
1990年 | 490篇 |
1989年 | 463篇 |
1988年 | 467篇 |
1987年 | 424篇 |
1986年 | 357篇 |
1985年 | 436篇 |
1984年 | 576篇 |
1983年 | 424篇 |
1982年 | 425篇 |
1981年 | 276篇 |
1980年 | 221篇 |
1979年 | 193篇 |
1978年 | 105篇 |
1977年 | 59篇 |
1976年 | 51篇 |
1975年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Methenamine-Silver Staining: a Simple and Sensitive Staining Method for Senile Plaques and Neurofibrillary Tangles 总被引:1,自引:0,他引:1
Chie Haga Kenji Ikeda Kiyoshi Iwabuchi Haruhiko Akiyama Hiromi Kondoh Kenji Kosaka 《Biotechnic & histochemistry》1994,69(5):295-300
An improved methenamine-silver impregnation method is presented which exhibits sensitivity for amyloid substances comparable to that of anti-β protein immunostaining. In optimally treated sections, this technique stained both β-amyloid deposits and neurofibrillary tangles, which are known to have a β-pleated structure. This simple procedure allows a large number of sections to be stained for routine examination. 相似文献
992.
K. Pomeroy D. C. W. Brown Y. Takahata 《In vitro cellular & developmental biology. Plant》1994,30(4):196-203
Summary Microspore-derived embryos fromBrassica napus cv. Topas (low erucic acid) and Reston (high erucic acid) were subjected to treatment with abscisic acid (ABA) during late-stage
embryo development and then dried under controlled relative humidities to mature dry seed levels of moisture. Exogenously
medium-supplied ABA arrested growth and development, reduced moisture content, increased total fatty acids on a dry weight
basis, and stimulated systhesis of proteins in microspore-derived embryos. ABA also resulted in a higher proportion of 22∶1
in cv. Reston (high 22∶1) and increased the level of fatty acid unsaturation in cv. Topas (low 22∶1). The accumulation of
two proteins that co-migrated with cruciferin and napin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two-dimensional
gels were also promoted by exposure to ABA, and the degree of accumulation was dependent on the concentration and time of
application of ABA. Controlled desiccation of microspore embryos, used to simulate normal maturation and dehydration of zygotic
embryos during seed development, did not seem to cause an increase of either storage proteins, total fatty acids, or 22∶1
(in cv. Reston), suggesting that dehydration is not a prerequisite for these processes, at least in culturedBrassica embryos. 相似文献
993.
ANTONIO OSUNA NIEVES RODRIGUEZ-CABEZAS FRANCISCO GAMARRO CARMEN MASCARO 《The Journal of eukaryotic microbiology》1994,41(3):231-236
ABSTRACT. We have studied the action of diphtheria toxin, modeccin and ricin on HeLa cells infected by Trypanosoma cruzi . Parasitized HeLa cells were resistant to diphtheria toxin and modeccin, whereas non-parasitized cells from the same cultures and control cultures showed cytopathological alterations. Protein synthesis, assayed by the incorporation of labelled methionine, diminished in toxin-treated control cultures but remained unaltered in the infected ones, compared to synthesis by untreated infected cells. Ricin, on the other hand, is a toxin that enters the cytoplasm by endocytosis. It has greater cytopathological effects in parasitized cells than in non-parasitized ones from the same cultures or uninfected control cells. Protein synthesis was inhibited in infected cultures treated with ricin. 相似文献
994.
Ralph Rapley 《Molecular biotechnology》1994,2(3):295-298
The polymerase chain reaction (PCR) is a powerful core molecular biology technique, which when coupled to chain termination
sequencing allows gene and DNA sequence information to be derived rapidly. A number of modifications to the basic PCR format
have been developed in an attempt to increase amplification efficiency and the specificity of the reaction. We have applied
the use of DNA-binding protein, gene 32 protein from bacteriophage T4 (T4gp32) to increase amplification efficiency with a
number of diverse templates. In addition, we have found that using single-stranded DNA-binding protein (SSB) or recA protein
in DNA sequencing reactions dramatically increases the resolution of sequencing runs. The use of DNA-binding proteins in amplification
and sequencing may prove to be generally applicable in improving the yield and quality of a number of templates from various
sources. 相似文献
995.
Manuela Aragno Elena Tamagno Giuseppe Poli Giuseppe Boccuzzi Enrico Brignardello Oliviero Danni 《Free radical research》1994,21(6):427-435
Dehydroepiandrosterone (DHEA), a lipid soluble steroid, administered to rats (100 mg/kg b.wt) by a single intraperitoneal injection, increases to twice its normal level in the liver microsomes. Microsomes so enriched become resistant to lipid peroxidation induced by incubation with carbon tetrachloride in the presence of a NADPH-regenerating system: also the lipid peroxidation-dependent inactivation of glucose-6-phosphatase and gamma-glutamyl transpetidase due to the haloalkane are prevented. Noteworthy, the liver microsomal drug-metabolizing enzymes and in particular the catalytic activity of cytochrome P450IIE1, responsible for the CCl4-activation, are not impaired by the supplementation with the steroid. Consistently, in DHEA-pretreated microsomes the protein covalent binding of the trichloromethyl radical (CCl3°), is similar to that of not supplemented microsomes treated with CCl4. It thus seems likely that DHEA protects liver microsomes from oxidative damage induced by carbon tetrachloride through its own antioxidant properties rather than inhibiting the metabolism of the toxin. 相似文献
996.
997.
998.
刘支前 《植物生理与分子生物学学报》1994,(3)
除草剂普杀特(Imazethapyr)对玉米根尖蛋白质和DNA合成的影响刘支前(北京农业大学农业应用化学系,北京100094)关键词:普杀特,玉米,蛋白质,DNA80年代美国氰胺公司开发的咪唑淋酮类除草剂,由于其高效低毒、杀草谱广,又因对某些农作物具... 相似文献
999.
小麦初生叶接种条锈菌毒性生理小种(CY29)及其弱毒突变菌系(CY29-mut3)后,呈不亲和反应的寄主叶片可溶性蛋白质合成能力在接种后24h显著高于未接种对照,但其后逐渐降低,直至接近对照;而呈亲和性反应的寄主叶片可溶性蛋白质合成在侵染早期与对照相近,但与膜结合蛋白质在96h时大大高于对照。对接种叶中核糖体的密度梯度分析证实:呈不亲和反应寄主叶片游离多聚核糖体及亲和反应的寄主内与膜结合多聚核糖体均有特异性增加。上述结果表明寄主的抗病和感病反应均与蛋白质合成能力的变化有关。 相似文献
1000.
Bo Skaaning Jensen Flemming Jessen Else K. Hoffmann 《The Journal of membrane biology》1993,131(3):161-178
Summary Net Cl– uptake as well as unidirectional36Cl influx during regulatory volume increase (RVI) require external K+. Half-maximal rate of bumetanide-sensitive36Cl uptake is attained at about 3.3mm external K+. The bumetanide-sensitive K+ influx found during RVI is strongly dependent on both Na+ and Cl–. The bumetanide-sensitive unidirectional Na+ influx during RVI is dependent on K+ as well as on Cl–. The cotransporter activated during RVI in Ehrlich cells, therefore, seems to transport Na+, K+ and Cl–. In the presence of ouabain and Ba+ the stoichiometry of the bumetanide-sensitive net fluxes can be measured at 1.0 Na+, 0.8 K+, 2.0 Cl– or approximately 1 : Na, 1 : K, 2 : Cl. Under these circumstances the K+ and Cl– flux ratios (influx/efflux) for the bumetanide-sensitive component were estimated at 1.34 ±0.08 and 1.82 ± 0.15 which should be compared to the gradient for the Na+, K+, 2Cl– cotransport system at 1.75 ± 0.24.Addition of sucrose to hypertonicity causes the Ehrlich cells to shrink with no signs of RVI, whereas shrinkage with hypertonic standard medium (all extracellular ion concentrations increased) results in a RVI response towards the original cell volume. Under both conditions a bumetanide-sensitive unidirectional K+ influx is activated. During hypotonic conditions a small bumetanide-sensitive K+ influx is observed, indicating that the cotransport system is already activated.The cotransport is activated 10–15 fold by bradykinin, an agonist which stimulates phospholipase C resulting in release of internal Ca2+ and activation of protein kinase C.The anti-calmodulin drug pimozide inhibits most of the bumetanide-sensitive K+ influx during RVI. The cotransporter can be activated by the phorbol ester TPA. These results indicate that the stimulation of the Na+, K+, Cl– cotransport involves both Ca2+/calmodulin and protein kinase C. 相似文献