全文获取类型
收费全文 | 44070篇 |
免费 | 119篇 |
国内免费 | 149篇 |
专业分类
系统科学 | 232篇 |
丛书文集 | 852篇 |
教育与普及 | 131篇 |
理论与方法论 | 243篇 |
现状及发展 | 19769篇 |
研究方法 | 1659篇 |
综合类 | 20934篇 |
自然研究 | 518篇 |
出版年
2013年 | 292篇 |
2012年 | 589篇 |
2011年 | 1105篇 |
2010年 | 304篇 |
2008年 | 764篇 |
2007年 | 767篇 |
2006年 | 804篇 |
2005年 | 819篇 |
2004年 | 785篇 |
2003年 | 777篇 |
2002年 | 769篇 |
2001年 | 1246篇 |
2000年 | 1172篇 |
1999年 | 802篇 |
1994年 | 381篇 |
1992年 | 737篇 |
1991年 | 615篇 |
1990年 | 669篇 |
1989年 | 641篇 |
1988年 | 650篇 |
1987年 | 688篇 |
1986年 | 702篇 |
1985年 | 836篇 |
1984年 | 652篇 |
1983年 | 580篇 |
1982年 | 501篇 |
1981年 | 491篇 |
1980年 | 617篇 |
1979年 | 1333篇 |
1978年 | 1156篇 |
1977年 | 1117篇 |
1976年 | 815篇 |
1975年 | 927篇 |
1974年 | 1289篇 |
1973年 | 1107篇 |
1972年 | 1150篇 |
1971年 | 1447篇 |
1970年 | 1798篇 |
1969年 | 1416篇 |
1968年 | 1332篇 |
1967年 | 1326篇 |
1966年 | 1147篇 |
1965年 | 835篇 |
1959年 | 482篇 |
1958年 | 787篇 |
1957年 | 623篇 |
1956年 | 529篇 |
1955年 | 484篇 |
1954年 | 517篇 |
1948年 | 333篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
261.
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
262.
Ph. van den Bosch de Aguilar Ch. Langhendries-Wéverberg J. Goemaere-Vanneste F. Flament-Durand J. P. Brion A. M. Couck 《Cellular and molecular life sciences : CMLS》1984,40(4):402-403
Summary Senile dementia of the Alzheimer type (SDAT) is a major problem in the human senescent population. As this pathology cannot be reproduced in animals, research into its development is greatly impeded. The technique of implantation of the nervous tissue has been utilized in order to establish an animal model and to test the possible existence of a transmissible agent. When human temporal cortex with Alzheimer's disease is implanted in the occipital cortex of 7-week-old rats, human cerebral tissue containing abundant tangles induces in the receiver cortex a reactive fibrous gliosis. In the processes of the astrocytes, twisted filaments are evident among bundles of normal filaments. These alterations could be induced by the metabolising of abnormal filament subunits or by some infectious agent introduced by the implant.This study is supported by grant No. 2.4517.82 of Fonds de la Recherche Fondamentale Collective of Belgium. 相似文献
263.
264.
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
265.
Summary In the rat, prolonged activation of 1-adrenoceptors causes a gain in salivary gland weight, whereas prolonged blockade of these receptors causes a reduction in weight.This work was supported by grants to J.E. from the Medical Faculty in Lund and the Swedish Medical Research Council (05927). 相似文献
266.
F. M. Goñi J. M. Valpuesta M. C. Barbero E. Rial J. I. G. Gurtubay J. M. Macarulla 《Cellular and molecular life sciences : CMLS》1984,40(2):193-195
Summary The solubilizing effect of Triton X-100 on beef heart submitochondrial particles (ETPH) has been studied under various physiological conditions. Coupled, uncoupled and azide-inhibited ETPH particles have been studied. Quantitative and qualitative differences are found in the proteins solubilized by the detergent from ETPH particles under the various conditions tested.Acknowledgments: This work was supported in part by a grant from a Spanish Comisión Asesora para la Investigación Cientifica y Técnica. M.C. Barbero was recipient of a scholarship from the Basque Government. 相似文献
267.
Effect of hormones and cyclic AMP on γ-glutamyltranspeptidase activity of rat mammary gland explants
M. P. Valdivieso J. F. Puente M. Sapag-Hagar 《Cellular and molecular life sciences : CMLS》1984,40(7):710-711
Summary -Glutamyl transpeptidase activity was assayed in midpregnant rat mammary gland explants at 14, 22 and 38 h, in the presence and absence of insulin, prolactin and corticosterone. With these 3 hormones the explants attained the characteristics of a secretory gland after 22 h of tissue culture, at which time the enzyme exhibited its maximal activity. The addition of dibutyryl cyclic AMP in the presence of the 3 hormones produced a significant increase in enzyme activity, which was maximal with a 1 mM concentration of the cyclic nucleotide. A similar effect was observed when theophylline or theophylline plus dibutyryl cyclic AMP were added to the culture medium.This work was supported by grant B1138-8333 from the Departamento de Desarrollo de la Investigación, Universidad de Chile. 相似文献
268.
269.
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
270.