全文获取类型
收费全文 | 32284篇 |
免费 | 134篇 |
国内免费 | 297篇 |
专业分类
系统科学 | 431篇 |
丛书文集 | 538篇 |
教育与普及 | 130篇 |
理论与方法论 | 105篇 |
现状及发展 | 13042篇 |
研究方法 | 1178篇 |
综合类 | 16638篇 |
自然研究 | 653篇 |
出版年
2013年 | 353篇 |
2012年 | 615篇 |
2011年 | 1262篇 |
2010年 | 433篇 |
2009年 | 420篇 |
2008年 | 730篇 |
2007年 | 832篇 |
2006年 | 815篇 |
2005年 | 749篇 |
2004年 | 662篇 |
2003年 | 542篇 |
2002年 | 545篇 |
2001年 | 858篇 |
2000年 | 923篇 |
1999年 | 638篇 |
1994年 | 341篇 |
1992年 | 490篇 |
1991年 | 419篇 |
1990年 | 472篇 |
1989年 | 439篇 |
1988年 | 429篇 |
1987年 | 462篇 |
1986年 | 449篇 |
1985年 | 542篇 |
1984年 | 435篇 |
1983年 | 381篇 |
1982年 | 354篇 |
1981年 | 342篇 |
1980年 | 405篇 |
1979年 | 879篇 |
1978年 | 721篇 |
1977年 | 700篇 |
1976年 | 533篇 |
1975年 | 658篇 |
1974年 | 844篇 |
1973年 | 737篇 |
1972年 | 734篇 |
1971年 | 910篇 |
1970年 | 1027篇 |
1969年 | 886篇 |
1968年 | 881篇 |
1967年 | 848篇 |
1966年 | 755篇 |
1965年 | 551篇 |
1959年 | 304篇 |
1958年 | 524篇 |
1957年 | 407篇 |
1956年 | 321篇 |
1955年 | 335篇 |
1954年 | 313篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
M. Rizzardini A. Ferraroli D. Dal Fiume L. Cantoni 《Cellular and molecular life sciences : CMLS》1984,40(12):1390-1392
Summary Im male rats hepatic cytochromes b5 and P-450 were reduced at different times after treatment with cyclophosphamide (CP) (200 mg/kg i.p. for 3 days). In contrast, microsomal heme did not change until 48 h after the last dose of CP, leading to accumulation of heme in a non-cytochromal form. Parallel to the above changes the heme metabolism showed derangement: -aminolaevulinate synthase, the rate-limiting enzyme in heme synthesis, was depressed and heme oxygenase, the enzyme which catalyzes the oxidative degradation of heme, was increased. 相似文献
142.
Summary Hexoprenaline potentiated the14C-aminopyrine uptake (a reliable index of H+ generation) of isolated rat gastric cells stimulated by 10–6–10–4 mol/l carbachol, and inhibited that in response to 10–4 mol/l histamine without and in the presence of propranolol. It is concluded that hexoprenaline acts as a partial agonist on parietal cell H2-receptors and that -adrenoceptor activation may functionally modualte gastric acid secretion.Acknowledgments. S. Maliski, Institute of Rheumatology, Warszawa, held a fellowship of the Alexander v. Humboldt-Foundation. The study was supported by the Deutsche Forschungsgemeinschaft. The skilful technical assistance of Mrs R. Maier and Mr R. Beer is gratefully acknowledged. 相似文献
143.
144.
Summary The intensity of sound-induced convulsions in the genetically epilepsy-prone rat (GEPR) was reduced in a dose related fashion by intracerebroventricular administration of dobutamine, (1 agonist), terbutaline (2 agonist) or phenylephrine (1 agonist). BHT-920 (2 agonist) did not cause a dose-related decrease in sound-induced convulsion intensity. Binding studies showed that whole brain and receptor densities (Bmax) were normal while the Kd was increased for the ligand in GEPR brain.Acknowledgment. We are most grateful to Boehringer Ingelheim for generously supplying BHT 920. We are also indebted to Ciba-Geigy Corporation for the gift of terbutaline hydrochloride and phentolamine hydrochloride. The work was supported in part by NIH grant NS 16829. 相似文献
145.
The cold dark interstellar Taurus Molecular Cloud One (TMC-1) is a rich source of acetylenic and polyacetylenic molecular species. As well as linear closed-shell molecules (H(C triple bond C)nCN) and symmetric rotors (CH3C triple bond CH, CH3C triple bond CCN), several radicals (C triple bond CH, C triple bond CCN, (C triple bond C2H) have also been identified, many of which had not been studied previously in the laboratory. Whether the observed abundances can be understood in terms of purely gas-phase ion-molecule chemical schemes, which produce reasonable agreement for the simplest polyatomic species, is unclear; alternative models involving the particulate interstellar grains as catalysts or sources have also been suggested. We now report the detection in TMC-1 of a new molecule, tricarbon monoxide (C3O), whose pure rotational spectrum has only very recently been studied in the laboratory. As C3O is the first known interstellar carbon chain molecule to contain oxygen, its existence places an important new constraint on chemical schemes for cold interstellar clouds. In fact, the observed abundance of tricarbon monoxide fits quite well into our model of galactochemistry. 相似文献
146.
Summary Resting oxygen consumption of the vascularly isolated gracilis anticus muscle of the rat perfused by natural circulation via the femoral artery with diluted or undiluted blood depends on oxygen delivery (the product of flow rate and arterial oxygen concentration-DO2) only when DO2 falls below 16 l/min/g. 相似文献
147.
F. V. DeFeudis L. M. Orensanz Muñoz M. A. Vidal G. Corrochano M. Sanchez del Alamo 《Cellular and molecular life sciences : CMLS》1978,34(9):1169-1170
Summary High-affinity, Na+-independent binding of -alanine to a synaptosomal fraction of rat brain was potently inhibited by glycine and by some other -amino acids, but not by taurine or GABA. This binding mechanism, which was also sensitive to both bicuculline and strychnine, might involve synaptic receptors for both -alanine and glycine.This study was supported in part by Centro Ramón y Cajal and Fundacion Juan March. 相似文献
148.
H. Kemona J. Prokopowicz N. Wotosowicz 《Cellular and molecular life sciences : CMLS》1978,34(2):257-257
Summary It has been shown that there is a higher count of blood platelets and thrombopoietic activity of plasma in women than men. 相似文献
149.
M Debray-Sachs M Dy H Aurengo B Descamps 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1978,286(2):249-252
CBA Mice were immunized by two intraperitoneal injections of 30 X 10(6) DBA/2 or C57BL/6 spleen cells at days--12 and--2. Peritoneal cell population was obtained at day zero by washing the peritoneal cavity of Mice. Adherent cells were then separated using a 2 hrs. incubation in "Falcon" plates followed by washing. This macrophage-rich peritoneal cell population was found nonspecifically cytotoxic against 51Cr labeled tumoral target cells: P815 X DBA/2 mastocytoma cells, EL4 X C57BL/L lymphoma cells and spontaneous lymphoma AKR cells (same H--2k as CBA). This adherent peritoneal cell cytoxicity was demonstrated after 24 hrs. incubation with the target cells. It was found in nonspecific combination as well as when using target cells syngeneic to the donor. These findings suggest that adherent peritoneal cell cytotoxicity could be at least partly due to macrophages and result from factor (s) released by sensitized lymphocytes in vivo in the same way as has been previously demonstrated in vitro. 相似文献
150.
The glycoprotein CEA (carcinoembryonic antigen) carries carbohydrate groups, which react with the plant lectins from Agaricus bisporus, Arachis hypogaea (peanut), with Tridacnin from invertebrate clams and with the anti-A lectins from snails. Accordingly, it has cryptantigenic structures, which correspond to the T or T-like antigen, the Tridacnin receptor and to the so called A-like antigen. 相似文献