全文获取类型
收费全文 | 31126篇 |
免费 | 80篇 |
国内免费 | 121篇 |
专业分类
系统科学 | 302篇 |
丛书文集 | 563篇 |
教育与普及 | 98篇 |
理论与方法论 | 94篇 |
现状及发展 | 14548篇 |
研究方法 | 1132篇 |
综合类 | 14291篇 |
自然研究 | 299篇 |
出版年
2012年 | 350篇 |
2011年 | 680篇 |
2009年 | 178篇 |
2008年 | 485篇 |
2007年 | 550篇 |
2006年 | 488篇 |
2005年 | 521篇 |
2004年 | 546篇 |
2003年 | 558篇 |
2002年 | 489篇 |
2001年 | 914篇 |
2000年 | 951篇 |
1999年 | 574篇 |
1994年 | 362篇 |
1992年 | 536篇 |
1991年 | 426篇 |
1990年 | 513篇 |
1989年 | 475篇 |
1988年 | 476篇 |
1987年 | 494篇 |
1986年 | 519篇 |
1985年 | 619篇 |
1984年 | 429篇 |
1983年 | 430篇 |
1982年 | 381篇 |
1981年 | 411篇 |
1980年 | 467篇 |
1979年 | 986篇 |
1978年 | 815篇 |
1977年 | 791篇 |
1976年 | 614篇 |
1975年 | 699篇 |
1974年 | 965篇 |
1973年 | 823篇 |
1972年 | 794篇 |
1971年 | 1016篇 |
1970年 | 1180篇 |
1969年 | 1025篇 |
1968年 | 939篇 |
1967年 | 910篇 |
1966年 | 786篇 |
1965年 | 589篇 |
1964年 | 208篇 |
1959年 | 339篇 |
1958年 | 571篇 |
1957年 | 418篇 |
1956年 | 346篇 |
1955年 | 347篇 |
1954年 | 333篇 |
1948年 | 232篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
991.
轮腿结合步态稳定裕度的研究 总被引:1,自引:1,他引:0
研究一种轮腿结合式步行机的步态特性和静态稳定裕度与步态参数间的关系,并对这类步态进行了计算机仿真。 相似文献
992.
993.
E. Bonilla M. Salazar J. Estevez H. Hernández P. Rangel 《Cellular and molecular life sciences : CMLS》1984,40(8):868-869
Summary After i.p. inoculation with the Guajira strain of Venezuelan equine encephalomyelitis virus a significant decrease in the density of (3H) spiroperidol binding sites in the striatum, midbrain and frontal cortex was observed. No changes in the affinity of the receptors could be demonstrated. This finding is compatible with neuronal degeneration caused by the viral infection.Acknowledgments. This work was partially supported by Condes-Luz and Fundacite-Zulia. Butaclamol isomers were a gift of Ayerst Laboratories, Montreal, Canada. 相似文献
994.
Comparative distribution of vasoactive intestinal polypeptide (VIP), substance P and PHI in the enteric sphincters of the cat 总被引:2,自引:0,他引:2
G P McGregor A E Bishop M A Blank N D Christofides Y Yiangou J M Polak S R Bloom 《Experientia》1984,40(5):469-471
In the feline gastrointestinal tract, the neuropeptides, substance P, VIP and PHI were investigated by specific radioimmunoassays and immunocytochemistry. The concentrations of all 3 peptides and the level of peptidergic innervation were significantly less in the anal sphincter than elsewhere, whereas no significant differences were seen between other sphincter and non-sphincter regions. 相似文献
995.
996.
An increase in venous pressure in the rat tail is known to result in acute edema. Acute venous stasis edema of the rat tail was induced by applying a force-controlled banding of standard tension (200 g) proximally for a period of 6-12 h. The hemodynamic changes of acute venous stasis edema were evaluated using non-invasive plethysmography, fluorescence angiography, computer thermography and invasive radioactive microsphere techniques. It is shown here that reduction of tail circulation to 40% of the control value is followed by prolonged vascular disorder characterized by genesis of reversible edema, increased total blood flow to the tail and decreased local cutaneous blood flow, without affecting the general hemodynamics. The cutaneous circulation (decreased blood flow) seems to be principally involved in the edemogenic response, whereas the deeper vessels (hyperemia) may or may not play a determinant role in acute experimental venous stasis edema in rats. 相似文献
997.
G. P. Rao A. K. S. Baghel R. K. Singh K. S. Chatterji 《Cellular and molecular life sciences : CMLS》1984,40(11):1257-1258
Summary Crude coralloid root extract ofCycas revoluta showed significant antiviral activity against viruses of the tomato plant (PVX, PVY, TMV, TAV and TRSV) when applied 24 h before virus inoculation, or when mixed with different virus inocula before virus inocultion, in hypersensitive and systemic hosts. No such inhibition was observed when extract was applied 24 h after virus inoculation. TAV did not show any inhibitory response in a systemic host.Authors are thankful to Dr S. N. Gupta and Dr (Smt.) K. Shukla for their valuable guidance and providing laboratory facilities and U.G.C. for financial assistance. 相似文献
998.
Summary The eggs of a sea hare,Aplysia kurodai, contained antibacterial factors which probably play a role in the defense of eggs against bacterial infection. The active factors were composed of several heat-labile proteins, unrelated to lysozyme, and were produced in the albumen gland. 相似文献
999.
Plasmodium falciparum strain-specific antibody blocks binding of infected erythrocytes to amelanotic melanoma cells 总被引:3,自引:0,他引:3
An important feature of Plasmodium falciparum malaria which differentiates it from other human malarias is that erythrocytes infected with trophozoites and schizonts are not present in the peripheral blood but are sequestered along capillary and venular endothelium. Infected erythrocytes attach via parasite-induced ultrastructural modifications on the surface of the infected cells, called 'knobs'. This sequestration may be important for parasite survival because it prevents infected erythrocytes from circulating through the spleen where they could be eliminated. We have established an in vitro correlate of sequestration and used it to demonstrate that immune sera from repeatedly infected Aotus monkeys inhibit binding of infected erythrocytes to endothelial cells. We have investigated whether antiserum that blocks binding of one isolate of P. falciparum to target cells can block or reverse binding of other isolates. We report here that sera which block or reverse binding are strain-specific, indicating that the corresponding antigens on the surface of the infected erythrocytes are strain (isolate)-specific. 相似文献
1000.
Summary Amniotic fluid was obtained from 19-day-old rat fetuses by aspiration. Pooled samples measured at 4 different dilutions demonstrated parallelism with standard rat TSH. It is concluded that rat amniotic fluid has TSH immunoactivity.This work was supported by Hong Kong University Research Grant No. 335/034/5727.The authors wish to acknowledge with thanks the gift of rat TSH RIA kit from Dr A. F. Parlow and the Rat Pituitary Programme of NIAMDD. 相似文献