全文获取类型
收费全文 | 5683篇 |
免费 | 212篇 |
国内免费 | 445篇 |
专业分类
系统科学 | 383篇 |
丛书文集 | 94篇 |
教育与普及 | 53篇 |
理论与方法论 | 4篇 |
现状及发展 | 431篇 |
综合类 | 5373篇 |
自然研究 | 2篇 |
出版年
2024年 | 48篇 |
2023年 | 73篇 |
2022年 | 110篇 |
2021年 | 111篇 |
2020年 | 107篇 |
2019年 | 100篇 |
2018年 | 103篇 |
2017年 | 115篇 |
2016年 | 121篇 |
2015年 | 129篇 |
2014年 | 254篇 |
2013年 | 205篇 |
2012年 | 333篇 |
2011年 | 301篇 |
2010年 | 215篇 |
2009年 | 359篇 |
2008年 | 320篇 |
2007年 | 420篇 |
2006年 | 417篇 |
2005年 | 406篇 |
2004年 | 345篇 |
2003年 | 257篇 |
2002年 | 261篇 |
2001年 | 205篇 |
2000年 | 180篇 |
1999年 | 145篇 |
1998年 | 110篇 |
1997年 | 99篇 |
1996年 | 78篇 |
1995年 | 60篇 |
1994年 | 65篇 |
1993年 | 53篇 |
1992年 | 53篇 |
1991年 | 49篇 |
1990年 | 33篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有6340条查询结果,搜索用时 0 毫秒
91.
92.
M.-C. Broillet 《Cellular and molecular life sciences : CMLS》1999,55(8-9):1036-1042
The transfer of a nitric oxide group to cysteine sulfhydryls on proteins, known as S-nitrosylation, is increasingly becoming
recognized as a ubiquitous regulatory reaction comparable to phosphorylation. It represents a form of redox modulation in
diverse tissues, including the brain. An increasing number of proteins have been found to undergo S-nitrosylation in vivo.
These proteins are called S-nitrosothiols, and may play an important role in many processes ranging from signal transduction,
DNA repair, host defense, and blood pressure control to ion channel regulation and neurotransmission. This review focuses
on the importance of the S-nitrosylation reaction and describes some recently identified S-nitrosothiols in various fields
of research. 相似文献
93.
Apolipoprotein E (apoE) ɛ4 allele is a genetic risk factor for late-onset familial and sporadic Alzheimer’s disease (AD).
In the central nervous system, apoE is secreted mainly by astrocytes as a constituent of high-density lipoproteins. A recent
study using apoE knockout mice provided strong evidence that apoE promotes cerebral deposition of amyloid β protein (Aβ).
However, no clear explanation of the pathogenesis of apoE-induced AD has been provided. Here we discuss two possible mechanisms
by which apoE might enhance Aβ deposition. One is the intracellular pathway in which apoE is internalized by neurons and induces
lysosomal accumulation of Aβ and amyloidogenic APP (amyloid precursor protein) fragments, leading to neuronal death. The other
is the extracellular pathway in which apoE-containing lipoproteins are trapped by Aβ1–42 deposits mobilizing soluble Aβ peptides
and consequently enlarge amyloid plaques. These two mechanisms may operate at different stages of AD pathogenesis and suggest
a chaperone-like function for the apoE molecule.
Received 4 February 1999; received after revision 9 April 1999; accepted 23 April 1999 相似文献
94.
MAP kinases in plant signal transduction 总被引:10,自引:0,他引:10
Mitogen-activated protein kinase (MAPK) pathways are modules involved in the transduction of extracellular signals to intracellular
targets in all eukaryotes. Distinct MAPK pathways are regulated by different extracellular stimuli and are implicated in a
wide variety of biological processes. In plants there is evidence for MAPKs playing a role in the signaling of abiotic stresses,
pathogens and plant hormones. The large number and divergence of plant MAPKs indicates that this ancient mechanism of bioinformatics
is extensively used in plants and may provide a new molecular handle on old questions. 相似文献
95.
Molecular cloning and sequence analysis of myosin genes from Arabidopsis thaliana and electron microscopic observation of a myosin from characean alga have revealed that overall structure of plant unconventional
myosins is similar to that of the class V myosins. These plant unconventional myosins have two heads, a coiled-coil tail of
varied length and a globular tail piece at the end. The tail piece is probably a site for membrane interaction. Characean
myosin is of special interest because it can translocate actin filaments at a velocity several times faster than muscle myosin,
which must have evolved to support the quick movement of animals in the struggle for their lives. 相似文献
96.
Summary The effect of intraperitonal cycloheximide administration on acid-soluble rat liver chromatin proteins has been investigated by electrophoresis in acetic acid-urea polyacrylamide gels. A nonhistone protein, which migrates between oxidized histone H3 and histone H1 has been found tobe increased in amount following cycloheximide treatment. This protein seems to be identical with semihistone protein H24 (uH2A). A possible relationship of uH2A to the inhibition of rRNA synthesis is discussed.This work was supported by the Turkish Scientific and Technical Research Council (TUBITAK) Project No. TAG 339 相似文献
97.
Summary Using two independent techniques, ultracentrifugation in a KBr-gradient, and native pore polyacrylamide gel electrophoresis in combination with [3H]-epoxyfarnesyldiazoacetate photoaffinity labeling, we showed that in the hemolymph ofPeriplaneta americana, and probably also inLeptinotarsa decemlineata JH-III binds to the lipophorin, whereas inLocusta migratoria JH-III binds to a different protein. 相似文献
98.
99.
Scarborough GA 《Cellular and molecular life sciences : CMLS》2000,57(6):871-883
Living cells require membranes and membrane transporters for the maintenance of life. After decades of biochemical scrutiny, the structures and molecular mechanisms by which membrane transporters catalyze transmembrane solute movements are beginning to be understood. The plasma membrane proton-translocating adenosine triphosphatase (ATPase) is an archetype of the P-type ATPase family of membrane transporters, which are important in a wide variety of cellular processes. The H+-ATPase has been crystallized and its structure determined to a resolution of 8 angstrom in the membrane plane. When considered together with the large body of biochemical information that has been accumulated for this transporter, and for enzymes in general, this new structural information is providing tantalizing insights regarding the molecular mechanism of active ion transport catalyzed by this enzyme. 相似文献
100.
从车辆动力学入手,分析含有弯度和坡度的路段对车辆行驶的影响,通过对N-S模型的修正得到了适用于弯路和坡路的元胞自动机模型,并且重新定义了弯路和坡路元胞的大小和更新规则。最后用改进的模型进行了仿真实验,仿真结果表明改进的模型能够更好的反映现实交通量之间的关系,证明了应用改进模型对弯路和坡路的仿真研究是可行的。 相似文献