全文获取类型
收费全文 | 58898篇 |
免费 | 4366篇 |
国内免费 | 138篇 |
专业分类
63402篇 |
出版年
2021年 | 417篇 |
2020年 | 355篇 |
2019年 | 396篇 |
2018年 | 908篇 |
2017年 | 859篇 |
2016年 | 1342篇 |
2015年 | 2038篇 |
2014年 | 2236篇 |
2013年 | 2885篇 |
2012年 | 3553篇 |
2011年 | 3377篇 |
2010年 | 2064篇 |
2009年 | 1615篇 |
2008年 | 2838篇 |
2007年 | 2894篇 |
2006年 | 2791篇 |
2005年 | 2676篇 |
2004年 | 2589篇 |
2003年 | 2424篇 |
2002年 | 2394篇 |
2001年 | 1610篇 |
2000年 | 1689篇 |
1999年 | 1373篇 |
1998年 | 576篇 |
1997年 | 460篇 |
1996年 | 439篇 |
1995年 | 412篇 |
1994年 | 431篇 |
1993年 | 386篇 |
1992年 | 866篇 |
1991年 | 826篇 |
1990年 | 795篇 |
1989年 | 755篇 |
1988年 | 704篇 |
1987年 | 637篇 |
1986年 | 620篇 |
1985年 | 591篇 |
1984年 | 550篇 |
1983年 | 489篇 |
1982年 | 455篇 |
1981年 | 471篇 |
1980年 | 362篇 |
1979年 | 538篇 |
1978年 | 430篇 |
1977年 | 373篇 |
1975年 | 417篇 |
1974年 | 412篇 |
1973年 | 374篇 |
1972年 | 380篇 |
1971年 | 351篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
A Schellenberger I Heinroth G Hübner 《Hoppe-Seyler's Zeitschrift für physiologische Chemie》1967,348(5):506-511
63.
Prostaglandin E2-9- oxoreductase (PGE2-9-OR), the enzyme which converts prostaglandin E2 (PGE2) to prostaglandin F2 alpha (PGF2 alpha), has been detected in human decidua vera. A 105-fold purification was achieved when the centrifuged homogenate was fractionated sequentially by DEAE-Trisacryl, hydroxyapatite-agarose gel, ultrogel AcA 44 and Matrex gel blue A gel chromatographies. The following kinetic constants for PGE2-9-OR have been obtained. The equilibrium constant with respect to PGE2 is 83 microM, the Michaelis constant, Km, for PGE2 is 80 microM, for NADPH 1.6 microM. The maximal velocity for the forward reaction is V1 = .203 pmol/min. The enzyme was inhibited by progesterone, oestradiol-17 beta, cortisol and pharmaceutical drugs. An activating effect could be demonstrated with Ca2+ and oxytocin. The occurrence of PGE2-9-OR in the decidua vera suggests that this enzyme may be responsible for the transformation of PGE2 to PGF2 alpha in these tissues. This may be an important mechanism for the initiation and maintenance of uterine contractions. 相似文献
64.
Dennis W. Jung Gerald P. Brierley 《Biochemical and biophysical research communications》1982,106(4):1372-1377
Heart mitochondria respiring in the presence of Pi release endogenous K+ to a sucrose medium when an uncoupler is added. The uncoupled mitochondria retain K+, however, if the oxidation of NAD(P)H is prevented by the addition of rotenone or antimycin. Addition of rotenone, once the uncoupler-dependent K+-efflux has been initiated, results in a rapid reduction of NAD(P) and a simultaneous decrease in permeability to K+. These changes are independent of respiration. The results suggest that a latent pathway for K+-permeability is present in the membrane, that it can be opened and closed reversibly, and that it reflects, either directly or indirectly, the redox status of mitochondrial pyridine nucleotides. The possible relationship of this putative pathway to those available for Ca2+ uptake and release is considered. 相似文献
65.
66.
67.
Dehalogenation of 4-chlorobenzoate by 4-chlorobenzoate dehalogenase from pseudomonas sp. CBS3: an ATP/coenzyme A dependent reaction 总被引:7,自引:0,他引:7
F L?ffler R Müller F Lingens 《Biochemical and biophysical research communications》1991,176(3):1106-1111
Pseudomonas sp. CBS3 was grown with 4-chlorobenzoate as sole source of carbon and energy. Freshly prepared cell-free extracts converted 4-chlorobenzoate to 4-hydroxybenzoate. After storage for 16 hours at 25 degrees C only about 50% of the initial activity was left. Treatment at 55 degrees C for 10 minutes, dialysis or desalting of the extracts by gel filtration caused a total loss of the activity of the 4-chlorobenzoate dehalogenase. The activity could be restored by the addition of ATP, coenzyme A and Mg2+. If one of these cofactors was missing, no dehalogenating activity was detectable. The amount of 4-hydroxybenzoate formed was proportional to the amount of ATP available in the test system whereas CoA served as a real coenzyme. A novel ATP/coenzyme A dependent reaction mechanism for the dehalogenation of 4-chlorobenzoate by 4-chlorobenzoate dehalogenase from Pseudomonas sp. CBS3 is proposed. 相似文献
68.
69.
Antioxidant effect of diethyldithiocarbamate on microsomal lipid peroxidation assessed by low-level chemiluminescence and alkane production 总被引:3,自引:0,他引:3
Different thiol-containing compounds, such as diethyldithiocarbamate (DDC), glutathione, penicillamine, and dithioerythritol have been chosen to study their effect on ascorbate/Fe-ADP-induced lipid peroxidation, detected by low-level chemiluminescence and alkane production. In the concentration range used, these thiols exerted a temporary protection against lipid peroxidation by lengthening the induction period; after overcoming this induction period, no substantial inhibition of either chemiluminescence or alkane production was observed. DDC was effective in protecting against lipid peroxidation in the nanomolar range, whereas the group of other thiol-containing molecules operated in the millimolar range. 相似文献
70.
S Bl?hser 《Histochemistry》1988,88(3-6):309-312
The ACTH-immunoreactive (ir) system of the avian brain is particularly conspicuous in the male white-crowned sparrow (Zonotrichia leucophrys gambelii). The irperikaryal population is concentrated mainly within the tuberal region, projecting primarily in a dorsal direction: (i) into the striatum; (ii) into rostral diencephalic, septal, hyperstriatal, and thalamic areas; and (iii) into dorsal and ventral areas of the brain stem. Ir-fibers seemingly contact local non-immunoreactive neurons mainly in the accumbens nucleus, septum, dorsal thalamic nuclei, infundibular and interpeduncular nuclei, and in the rostral diencephalon. Neurohemal zones are not supplied by ACTH-ir terminals. Immunocytochemical problems arising from the complexity of the proopiomelanocortin molecule and its derived peptide components are discussed in relation to phylogenetically directed studies, and contradictory results. 相似文献