全文获取类型
收费全文 | 5684篇 |
免费 | 518篇 |
专业分类
6202篇 |
出版年
2023年 | 27篇 |
2022年 | 65篇 |
2021年 | 129篇 |
2020年 | 71篇 |
2019年 | 125篇 |
2018年 | 130篇 |
2017年 | 119篇 |
2016年 | 192篇 |
2015年 | 297篇 |
2014年 | 288篇 |
2013年 | 358篇 |
2012年 | 468篇 |
2011年 | 403篇 |
2010年 | 249篇 |
2009年 | 229篇 |
2008年 | 305篇 |
2007年 | 301篇 |
2006年 | 268篇 |
2005年 | 265篇 |
2004年 | 240篇 |
2003年 | 216篇 |
2002年 | 172篇 |
2001年 | 104篇 |
2000年 | 98篇 |
1999年 | 111篇 |
1998年 | 62篇 |
1997年 | 51篇 |
1996年 | 58篇 |
1995年 | 46篇 |
1994年 | 32篇 |
1993年 | 39篇 |
1992年 | 57篇 |
1991年 | 71篇 |
1990年 | 69篇 |
1989年 | 42篇 |
1988年 | 48篇 |
1987年 | 45篇 |
1986年 | 41篇 |
1985年 | 40篇 |
1984年 | 21篇 |
1983年 | 21篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 17篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1972年 | 18篇 |
排序方式: 共有6202条查询结果,搜索用时 0 毫秒
1.
2.
Serum proteins [molecular weight (MW) > 10,000] are essential for increased insulin-stimulated glucose transport after in vitro muscle contractions. We investigated the role of the kallikrein-kininogen system, including bradykinin, which is derived from kallikrein (MW > 10,000)-catalyzed degradation of serum protein kininogen (MW > 10,000), on this contraction effect. In vitro electrical stimulation of rat epitrochlearis muscles was performed in 1) rat serum +/- kallikrein inhibitors; 2) human plasma (normal or kallikrein-deficient); 3) rat serum +/- bradykinin receptor-2 inhibitors; or 4) serum-free buffer +/- bradykinin. 3-O-methylglucose transport (3-MGT) was measured 3.5 h later. Serum +/- kallikrein inhibitors tended (P = 0.08) to diminish postcontraction insulin-stimulated 3-MGT. Contractions in normal plasma enhanced insulin-stimulated 3-MGT vs. controls, but contractions in kallikrein-deficient plasma did not. Supplementing rat serum with bradykinin receptor antagonist HOE-140 during contraction did not alter insulin-stimulated 3-MGT. Muscles stimulated to contract in serum-free buffer plus bradykinin did not have enhanced insulin-stimulated 3-MGT. Bradykinin was insufficient for postcontraction-enhanced insulin sensitivity. However, results with kallikrein inhibitors and kallikrein-deficient plasma suggest kallikrein plays a role in this improved insulin action. 相似文献
3.
4.
A pertussis toxin-sensitive G-protein mediates some aspects of insulin action in BC3H-1 murine myocytes. 总被引:9,自引:0,他引:9
L Luttrell E Kilgour J Larner G Romero 《The Journal of biological chemistry》1990,265(28):16873-16879
The involvement of G-proteins in the insulin signal transduction system has been studied in detail using the murine BC3H-1 myocyte system. Pertussis toxin (PT) treatment, previously shown to attenuate some of the metabolic effects of insulin in this cell line (Luttrell, L.M., Hewlett, E.L., Romero, G., and Rogol, A.D. (1988) J. Biol. Chem. 263, 6134-6141), abolished insulin-induced generation of diacylglycerol and inositolglycan mediators with no effects on either the autophosphorylation of the insulin receptor or the phosphorylation of the major endogenous substrates for insulin-stimulated tyrosine kinase activity (pp185 and pp42-45). In vitro ADP-ribosylation and immunoblotting studies suggest that the major PT substrate is a 40-kDa protein of the G alpha family. This protein band did not exhibit detectable tyrosine phosphorylation upon stimulation of either intact cells or cell membranes with insulin. In the presence of low concentrations of GTP, insulin treatment of isolated myocyte plasma membranes resulted in a small (30-40%) but significant stimulation of GTP hydrolysis. This effect was best observed in the presence of small concentrations of sodium dodecyl sulfate. The rate of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) binding to BC3H-1 membranes was also significantly increased in the presence of insulin. The effects of insulin on GTP hydrolysis and GTP gamma S binding were found to be dependent on the concentration of insulin. These effects were not detected in plasma membranes prepared from PT-pretreated BC3H-1 myocytes. In contrast, pretreatment with the B (inactive) subunit of PT did not alter the response of myocyte membranes to insulin. High affinity binding of [125I]iodoinsulin to myocyte plasma membranes was reduced by 60-70% in the presence of guanine nucleotides. Similar effects on insulin binding were produced by PT pretreatment of the cells. In contrast, adenine nucleotides had no effect on insulin binding. Scatchard analysis of the binding data showed that the observed effects of guanine nucleotides and PT on insulin binding resulted either from a reduction in the number of high affinity insulin binding sites or from a significant reduction of the affinity of insulin for its receptor. Low affinity binding sites did not appear to be affected by either guanine nucleotides nor PT pretreatment. These results provide substantial evidence suggestive of a noncovalent interaction between the insulin receptor and a regulatory G-protein system during the process of insulin signaling. 相似文献
5.
Nikolas K. Haass D. Ripperger E. Wladykowski P. Dawson P. A. Gimotty C. Blome F. Fischer P. Schmage I. Moll Johanna M. Brandner 《Histochemistry and cell biology》2010,133(1):113-124
Melanoma depends on, interacts with and reacts to the stroma in which it is embedded, including fibroblasts, extracellular
matrix, endothelial cells and immune cells. However, the impact of melanoma on the epidermal tumor microenvironment—the multilayered
epithelium of the skin—is poorly understood. Gap junctions are essential for intercellular communication and involved in proliferation,
differentiation and homeostasis of keratinocytes. We have shown previously that the gap junction proteins connexin 26 and
30 (Cx26 and Cx30) are induced in the epidermal tumor microenvironment of skin cancers including melanoma. This study compares
the extent of Cx26, Cx30 and Cx43 expression in the epidermal microenvironment of melanocytic nevi and melanomas and its association
with melanoma thickness, proliferative index of the tumor and its microenvironment, and with 5-year metastasis and survival.
We found that induction of Cx26 and Cx30 cell–cell border expression in the epidermal tumor microenvironment correlates to
malignancy. Importantly, there was a significant correlation of tumor thickness with the vertical epidermal Cx26 and Cx30
expression pattern and the horizontal Cx26 dissemination. Furthermore, horizontal Cx26 expression correlated with metastasis.
Vertical epidermal expression patterns of Cx26 and Cx30 significantly correlated with the proliferative index in the epidermal
tumor microenvironment but not with the proliferative index in the tumor. In contrast, Cx43 did not correlate with malignancy,
thickness or proliferative index. In summary, here we show for the first time a significant association between the progression
of melanoma and alterations in its epithelial tumor microenvironment. 相似文献
6.
7.
Relationship between a 47-kDa cytoplasmic membrane polypeptide and nitrate transport in Anacystis nidulans 总被引:2,自引:0,他引:2
M N Sivak C Lara J M Romero R Rodríguez M G Guerrero 《Biochemical and biophysical research communications》1989,158(1):257-262
The polypeptide composition of cytoplasmic membranes of the cyanobacterium Anacystis nidulans changes in response to variations in the nitrogen source available to the cells, differing specifically in the amount of a polypeptide of 47-kDa molecular mass. Synthesis of the polypeptide and expression of nitrate transport activity are repressed by ammonium. Transfer of ammonium-grown cells to a medium containing nitrate as the sole nitrogen source results in parallel development of the 47-kDa polypeptide and nitrate transport activity of the cells. These results suggest the involvement of the 47-kDa cytoplasmic membrane polypeptide in nitrate transport by A. nidulans. 相似文献
8.
N. Romero C. Marsac M. Fardeau M. Droste B. Schneyder B. Kadenbach 《Histochemistry and cell biology》1990,94(2):211-215
Summary The immunohistochemical reaction of monoclonal as well as polyclonal antibodies against cytochrome c oxidase (COX) subunits
with serial sections of normal human skeletal muscle was investigated. The stronger reactivity of polyclonal antibodies to
COX subunits II–III and VIIbc with type I as compared to type II fibres, correlated well with the higher histochemical reactivity
of NADH dehydrogenase, succinate dehydrogenase and cytochrome c oxidase in type I fibres. In contrast an almost exclusive
reaction of a monoclonal antibody against subunit IV with type I fibre and a preponderan reaction of a polyclonal antibody
against subunits Vab with type II fibres was obtained. Antibodies against subuntis I, Vb and VIc did not reveal a fibre-type-specific
reactivity. The data indicate in human muscle the occurrence of fibre type-specific isozymes of cytochrome c oxidase differing
in subunits IV and Va or Vb. 相似文献
9.
A new species of land planarian preying on termites in Kenya (Platyhelminthes: Turbellaria: Tricladida: Terricola) 总被引:1,自引:0,他引:1
A new species of land planarian is described from Kenya. Microplana rermirophaga sp. nov. preys on termites by capturing them at the openings to their nest. The pharynx is unusually far forwards for a land planarian and this is probably related to the active nature of the prey. There is an anterior depression caused by the termination of parenchymal longitudinal muscle bundles which might act as a sucker. All specimens are immature which leads to some difficulty in assigning the species to a genus. 相似文献
10.
Romero Jorge Liras Paloma Martín Juan F. 《Applied microbiology and biotechnology》1988,27(5-6):510-516
Summary Seven mutants of Streptomyces clavuligerus blocked in the biosynthesis of clavulanic acid, cephamycin C, or both antibiotics, have been isolated and characterized. Mutants nca1 and nca2 were unable to synthesize clavulanic acid but produced cephamycin C. Mutants nce1 and nce2 were completely blocked in cephamycin C production but formed clavulanic acid. A third group (mutants ncc1, ncc4 and ncc5) failed to produce both antibiotics. Arginase activity (forming ornithine) was very low in mutants ncc1 and ncc5. All the mutants blocked in clavulanic acid biosynthesis showed a normal ornithine--aminotransferase activity. Mutant ncc1, blocked in cephamycin biosynthesis, lacked completely lysine--aminotransferase (forming -aminoadipic acid) and isopenicillin N synthase. Two other mutants (nce2 and nce5) lacked isopenicillin N synthase. There was a good correlation between the isopenicillin N synthase and the lysine--aminotransferase activities of the nca mutants and the ability of those strains to produce cephamycin C. The condensing enzyme involved in the formation of the clavulanic acid nucleus appears to be different from the isopenicillin N synthase.Dedicated to Professor H.-J. Rehm on the occasion of his 60th birthday 相似文献