全文获取类型
收费全文 | 2955篇 |
免费 | 202篇 |
国内免费 | 2篇 |
出版年
2023年 | 32篇 |
2022年 | 64篇 |
2021年 | 106篇 |
2020年 | 88篇 |
2019年 | 97篇 |
2018年 | 121篇 |
2017年 | 98篇 |
2016年 | 140篇 |
2015年 | 187篇 |
2014年 | 202篇 |
2013年 | 222篇 |
2012年 | 267篇 |
2011年 | 240篇 |
2010年 | 146篇 |
2009年 | 111篇 |
2008年 | 142篇 |
2007年 | 135篇 |
2006年 | 122篇 |
2005年 | 91篇 |
2004年 | 86篇 |
2003年 | 70篇 |
2002年 | 79篇 |
2001年 | 44篇 |
2000年 | 43篇 |
1999年 | 33篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有3159条查询结果,搜索用时 15 毫秒
21.
Effects of Controlled Atmospheres on Production of Sesquiterpenoid Stress Metabolites by White Potato Tuber: Possible Involvement of Cyanide-resistant Respiration 下载免费PDF全文
Levels of katahdinone (solavetivone), lubimin, rishitin, and phytuberin, sesquiterpenoid stress metabolites of white potato (Solanum tuberosum), were monitored in tuber slices which were challenged with an extract of Phytophthora infestans and incubated under controlled atmospheres. A mixture of ethylene in air enhanced stress metabolite production. This enhancement was amplified by higher partial pressures of oxygen. Stress metabolite production was inhibited by salicylhydroxamic acid. These results suggest the involvement of cyanide-resistant respiration in the production of potato stress metabolites, compounds which may serve as phytoalexins. 相似文献
22.
Kazu Kurosawa W.David Ollis Brian T. Redman Ian O. Sutherland Herbert M. Alves Otto R. Gottlieb 《Phytochemistry》1978,17(8):1423-1426
The absolute configurations of isoflavans and isoflavanquinones isolated from Cyclolobium, Dalbergia and Machaerium species were established by comparison of their ORD curves with that of (3S)-5,7,3′,4′-tetra-methoxyisoflavan and (3S)-7,4′-dimethoxyisoflavan-2′,5′-quinone, respectively. The assignments were checked by the ozonolysis of the isoflavan (?)-duartin to (R)-paraconic acid and the oxidation of isoflavans to isoflavanquinones. The PMR spectra of the dihydropyran ring of the isoflavans are discussed in terms of the preferred conformation of this ring. 相似文献
23.
The potentiometric acid-base titration curve of fully protonated lysozyme at ionic strengths of 0.10 and 1.0 m has been performed. The stoichiometry and the pKa values of each titratable group have been determined through the linearization of titration curves. Two types of carboxylic groups with pKa values of 3.76 and 5.02, the imidazole group with pKa 7.37 and the amine group with pKa 9.63, have been identified at an ionic strength of 0.10 m at 25.0°C. The number of titratable groups found per mole of protein has been 5.12 and 5.60 for the two types of carboxylic groups, 1.13 for the imidazole group, and 3.19 for the amino groups. The endpoint of the titration of the protein obtained by this method accords quite well with the endpoint obtained by the use of Gran function applied to the excess of strong base. 相似文献
24.
Expression and characterization of the N-terminal half of antistasin, an anticoagulant protein derived from the leech Haementeria officinalis 总被引:1,自引:0,他引:1
L O Palladino J S Tung C Dunwiddie K Alves A B Lenny C Przysiecki D Lehman E Nutt G C Cuca S W Law 《Protein expression and purification》1991,2(1):37-42
Antistasin, a 15-kDa anticoagulant protein isolated from the salivary glands of the Mexican leech Haementeria officinalis, has been shown to be a potent inhibitor of factor Xa in the blood coagulation cascade. Antistasin possesses a twofold internal homology between the N- and C-terminal halves of the molecule, suggesting a gene duplication event in the evolution of the antistasin gene. This structural feature also suggests that either or both halves of the protein may possess biological activity if expressed as separate domains. Because the N-terminal domain contains a factor Xa P1-reactive site, we chose to express this domain in an insect cell baculovirus expression system. Characterization of this recombinant half antistasin molecule reveals that the N-terminal domain inhibits factor Xa in vitro, with a K(i) of 1.7 nM. 相似文献
25.
The cytokineplast: purified, stable, and functional motile machinery from human blood polymorphonuclear leukocytes 总被引:11,自引:4,他引:7 下载免费PDF全文
We examined the formation of motile, chemotactically active, anucleate fragments from human blood polymorphonuclear leukocytes (PMN, granulocytes), induced by the brief application of heat. These granule-poor fragments are former protopods (leading fronts, lamellipodia) that become uncoupled from the main body of the cell and leave it, at first with a connecting filament that breaks and seals itself. The usual random orientation of such filaments can be controlled by preorientation of cells in a gradient of the chemotactic peptide, N-formylmethionylleucylphenylalanine (F-Met-Leu-Phe) (2x10(-9) M- 1x10(-8)). Cytochalsin B, 2.5-5 μg/ml, prevents fragment formation; colchicine, 10(-5) M, does not. In scanning electron micrographs, fragments are ruffled and the cell body rounded up and rather smooth. In transmission electron micrographs, fragments contain microfilaments but lack centrioles and microtubules. Like intact cells, both bound and free fragments can respond chemotactically to an erythrocyte destroyed by laser microirradiation (necrotaxis); the free, anucleate fragments may do so repeatedly, even after having been held overnight at ambient temperatures. We propse the name cytokineplast for the result of this self-purification of motile apparatus. The exodus of the motile machinery from the granulocyte requires anchoring of the bulk of the cell to glass and uncoupling, which may involve heat-induced dysfunction of the centrosome. In ultrastructural studies of the centrosomal region after heat, centriolar structure remains intact, but pericentriolar osmiophilic material appears condensed, and microtubules are sparse. These changes are found in all three blood cell types examined: PMN, eosinophil, and monocyte. Of these, the first two make fragments under our conditions; the more sluggish monocyte does not. Uncoupling is further linked to centrosomal dysfunction by the observation that colchicines-treated granulocytes (10(-5)M, to destroy the centrosome’s efferent arm) make fragments after less heat than controls. If motive force and orientation are specified mainly from the organelle-excluding leading front, then endoplasmic streaming in PMN is a catch-up phenomenon, and microtubules do not provide the vector of locomotion but rather stabilize and orient the “baggage” (nucleus, granuloplasm)—i.e., they prevent fishtailing. Moreover, constraints emanating from the centrosome may now be extended to include, maintenance of the motile machinery as an integral part of the cell. 相似文献
26.
Micro-buffy coats of whole blood: a method for the electron microscopic study of mononuclear cells 总被引:3,自引:0,他引:3
A method for the electron microscopic study of human peripheral lymphocytes by which very small buffy coats are obtained through centrifugation of heparinized whole blood in glass or plastic microhematocrit tubes is presented. This method is time saving and efficient, yielding well preserved material and a comparatively large number of mononuclear cells (mainly lymphocytes) in each thin section. 相似文献
27.
28.
Marcelo Rodrigues Thales H. F. Costa Reginaldo Alves Festucci-Buselli Luzimar Campos Silva Wagner Campos Otoni 《In vitro cellular & developmental biology. Plant》2012,48(1):67-72
In vitro propagation of neem (Azadirachta indica A. Juss.) may offer an efficient alternative to seed propagation of this species. For optimization of in vitro propagation, different basal salt formulations, growth regulators, and culture container sealants (polytetrafluoroethylene
hydrophobic membranes [PTFE]) were evaluated. Nodal segments cultured on Murashige and Skoog (MS) medium showed the highest
shoot formation per explant (1.67). Explants cultured in flasks containing MS medium with 0.5 mg L−1 benzyladenine, 0.5 mg L−1 kinetin, and 0.05 mg L−1 naphthaleneacetic acid, and sealed with two PTFE membranes, produced the highest number of shoots (4.04). In contrast, explants
cultured in flasks without membranes showed leaf chlorosis and senescence. For plant recovery, regenerants were acclimatized
in a substrate of coconut fiber and eucalyptus bark (1:1) and showed 80% survival. Our results indicated that the use of flasks
with vents was beneficial for in vitro propagation of this important plant. 相似文献
29.
Julie Dufour Aurélien Pommier Georges Alves Hugues De Boussac Corinne Lours-Calet David H. Volle Jean-Marc A. Lobaccaro Silvère Baron 《PloS one》2013,8(3)
Recent studies underline the implication of Liver X Receptors (LXRs) in several prostate diseases such as benign prostatic hyperplasia (BPH) and prostate cancer. In order to understand the molecular mechanisms involved, we derived epithelial cells from dorsal prostate (MPECs) of wild type (WT) or Lxrαβ−/− mice. In the WT MPECs, our results show that LXR activation reduces proliferation and correlates with the modification of the AKT-survival pathway. Moreover, LXRs regulate lipid homeostasis with the regulation of Abca1, Abcg1 and Idol, and, in a lesser extent, Srebp1, Fas and Acc. Conversely cells derived from Lxrαβ−/− mice show a higher basal phosphorylation and consequently activation of the survival/proliferation transduction pathways AKT and MAPK. Altogether, our data point out that the cell model we developed allows deciphering the molecular mechanisms inducing the cell cycle arrest. Besides, we show that activated LXRs regulate AKT and MAPK transduction pathways and demonstrate that LXRs could be good pharmacological targets in prostate disease such as cancer. 相似文献
30.