全文获取类型
收费全文 | 32025篇 |
免费 | 65篇 |
国内免费 | 126篇 |
专业分类
系统科学 | 431篇 |
丛书文集 | 686篇 |
教育与普及 | 82篇 |
理论与方法论 | 124篇 |
现状及发展 | 14175篇 |
研究方法 | 1422篇 |
综合类 | 14784篇 |
自然研究 | 512篇 |
出版年
2013年 | 193篇 |
2012年 | 486篇 |
2011年 | 1057篇 |
2010年 | 202篇 |
2009年 | 188篇 |
2008年 | 608篇 |
2007年 | 724篇 |
2006年 | 661篇 |
2005年 | 672篇 |
2004年 | 649篇 |
2003年 | 674篇 |
2002年 | 620篇 |
2001年 | 1013篇 |
2000年 | 996篇 |
1999年 | 618篇 |
1992年 | 578篇 |
1991年 | 460篇 |
1990年 | 512篇 |
1989年 | 461篇 |
1988年 | 442篇 |
1987年 | 483篇 |
1986年 | 503篇 |
1985年 | 582篇 |
1984年 | 453篇 |
1983年 | 399篇 |
1982年 | 345篇 |
1981年 | 398篇 |
1980年 | 453篇 |
1979年 | 1029篇 |
1978年 | 812篇 |
1977年 | 819篇 |
1976年 | 601篇 |
1975年 | 663篇 |
1974年 | 977篇 |
1973年 | 813篇 |
1972年 | 774篇 |
1971年 | 939篇 |
1970年 | 1231篇 |
1969年 | 977篇 |
1968年 | 826篇 |
1967年 | 930篇 |
1966年 | 784篇 |
1965年 | 556篇 |
1959年 | 336篇 |
1958年 | 531篇 |
1957年 | 370篇 |
1956年 | 335篇 |
1955年 | 287篇 |
1954年 | 288篇 |
1948年 | 194篇 |
排序方式: 共有10000条查询结果,搜索用时 687 毫秒
1.
ABSTRACTVideofilms of a foraging flying gurnard (Dactylopterus volitans) were collected at Itaipu, Niterói, RJ, Brazil. Analysis revealed details of the use of anterior parts of the pectoral fins which act as digging ‘hands’ to access infaunal prey items that are subsequently captured by oral suction feeding. Each pectoral fin has two distinct sections articulated separately on the pectoral girdle. The digging ‘anterior pectoral fin’ mainly consists of segmented and flexible fin rays but has an anterior robust unsegmented ray that provides an edge to the ‘hand’, allowing penetration of the substratum. The huge ‘posterior pectoral fins’ are supported by unsegmented rays. Most digging episodes involved one ‘hand’ and consisted of 1–7 cycles of movement with frequencies 1.15–3.74 cycles s?1. During a cycle, the ‘hand’ is moved forwards and medially above the substratum, then is twisted medially and simultaneously depressed so that the anterior unsegmented ray impacts and enters the substratum. The hand is then drawn backwards and laterally to disturb the substratum. To prevent upward pitching of the head during digging, the ‘posterior pectoral fins’ are both moved anteriorly and laterally to shift the centre of gravity forwards while the caudal and ?second dorsal fins continue to provide propulsive force. 相似文献
2.
系统地总结和介绍了我国高性能计算机,包括“银河”系列巨型机、“曙光”系列巨型机、“神威”系列巨型机、“深腾”系列巨型机以及“深超”系列巨型机的开发研制以及应用情况。 相似文献
3.
The shrink proofing on wool with treatment of protease named Argaenzyme STL was studied. The various pretreating auxiliaries, different parameters for protease treating process and the effect of stabilizer were discussed in detail. The varieties of some properties before and after protease treatment were also investigated. 相似文献
4.
Ten-day treatment with nicotine (5, 25 or 50 micrograms/ml drinking water) dose-dependently intensified gastric ulceration induced by cold-restraint, and emptying rate. Stomach contractions produced by graded doses of bethanechol i.v. were elevated further by nicotine treatment. It is suggested that chronic nicotine administration produces hypersensitivity of the gastric muscarinic receptors; stomach hypermotility contributes to the ulcer-worsening action of the alkaloid. 相似文献
5.
Photon emission of phagocytes in relation to stress and disease. 总被引:1,自引:0,他引:1
Phagocytes, the first-line cells of the body's defence mechanisms against invading pathogens, kill microorganisms by means of lysosomal degradative enzymes and highly toxic reactive oxygen intermediates. The reactive oxygen compounds are produced, in a process called the 'respiratory burst', by the NADPH oxidase complex in plasma membranes, and by myeloperoxidase in phagolysosomes after degranulation. These processes generate electronically excited states which, on relaxation, emit photons, giving rise to phagocyte chemiluminescence (CL). This paper describes the conditions for the measurement of CL, and reviews the activity of phagocytes from individuals undergoing stress or disease. The capability of phagocytes to emit photons reflects remarkably well the pathophysiological state of the host. In many cases even the magnitude of the stress, the presence of a pathogen in the body, or the activity of the disease can be estimated. Physiological changes, e.g. in the reproductive cycle, can also be predicted. 相似文献
6.
新的、高密度树木种植正在给林业生物技术带来迅速的变化。但是如果不能克服生态风险和经济障碍.这些新的方法或许永远也无法使用—— 相似文献
7.
8.
9.
W. Jadassohn E. Cherbuliez P. Boymond H. Isler 《Cellular and molecular life sciences : CMLS》1948,4(6):225-226
Summary The authors show the antibiotic activity of water-insoluble salts of hydrosoluble antibiotics in the case of penicillin G (salts of iron, copper, silver, gold, and uranium) and streptomycin (oleate). 相似文献
10.
1 Results Oxy-apatite materials are thought as zirconia-substitutes in Solid Oxide Fuel Cells due to their fast ionic conduction. However, the well known difficulties related to their densification prevent them from being used as such. This study presents strategies to obtain oxy-apatite dense materials and the influence of elaboration route on transport properties. Particular emphasis is put on the microstructure effect on ion conduction. By the combined use of freeze-drying and conventional or spark p... 相似文献