全文获取类型
收费全文 | 43087篇 |
免费 | 132篇 |
国内免费 | 151篇 |
专业分类
系统科学 | 328篇 |
丛书文集 | 868篇 |
教育与普及 | 79篇 |
理论与方法论 | 142篇 |
现状及发展 | 19129篇 |
研究方法 | 1640篇 |
综合类 | 20431篇 |
自然研究 | 753篇 |
出版年
2013年 | 300篇 |
2012年 | 575篇 |
2011年 | 1326篇 |
2010年 | 240篇 |
2008年 | 680篇 |
2007年 | 819篇 |
2006年 | 776篇 |
2005年 | 810篇 |
2004年 | 860篇 |
2003年 | 763篇 |
2002年 | 738篇 |
2001年 | 1259篇 |
2000年 | 1214篇 |
1999年 | 790篇 |
1992年 | 793篇 |
1991年 | 624篇 |
1990年 | 671篇 |
1989年 | 614篇 |
1988年 | 616篇 |
1987年 | 643篇 |
1986年 | 648篇 |
1985年 | 876篇 |
1984年 | 633篇 |
1983年 | 530篇 |
1982年 | 462篇 |
1981年 | 498篇 |
1980年 | 625篇 |
1979年 | 1373篇 |
1978年 | 1068篇 |
1977年 | 1026篇 |
1976年 | 858篇 |
1975年 | 914篇 |
1974年 | 1256篇 |
1973年 | 1068篇 |
1972年 | 1146篇 |
1971年 | 1304篇 |
1970年 | 1773篇 |
1969年 | 1384篇 |
1968年 | 1197篇 |
1967年 | 1240篇 |
1966年 | 1148篇 |
1965年 | 862篇 |
1964年 | 263篇 |
1959年 | 487篇 |
1958年 | 846篇 |
1957年 | 604篇 |
1956年 | 492篇 |
1955年 | 449篇 |
1954年 | 496篇 |
1948年 | 333篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
Humoral immune reactions to heat shock proteins (hsp) from microorganisms are one aspect of microbial infections in humans. The production of antibodies which are specific to epitopes present on procaryotic hsp leads also to the appearance of cross-reactive serum antibodies in the host organism that react with human hsp. This article discusses the consequences of such autoreactive antibodies for the host in context with the development of immune tolerance and autoimmune diseases, especially rheumatoid arthritis (RA), and in experimental animal models for arthritis such as adjuvant arthritis in rats. On the basis of epitope cross-reactivity between hsp and other host proteins, a hypothesis is presented for the development of autoimmune disease following the production of hsp-specific antibodies. 相似文献
15.
It was established that there is little diversity of bryophytes in the derived savanna. Mosses were found in the sampling sites, whereas liverworts were rarely observed. The reproductive methods of four dominant sexually reproducing savanna mosses —Archidium ohioense, Bryum coronatum, Fissidens minutifolius andTrachycarpidium tisserantii were monitored over two consecutive rainy seasons. Protonemal and gametophyte production were noticed in the field in March/April, and capsule dehiscence and spore dispersal occurred in September/October. The sequential stages of development, starting with gametangial production and ending with the falling of the dehisced capsules, occurred within the rainy season. However,A. ohioense andT. tisserantii did not discharge their spores easily (cleistocarpous), unlike the stegocarpous speciesB. coronatum andF. minutifolius. Water availability and possibly high humidity may have contributed to growth. The short period between sex organ formation and dehiscence of capsule seen in these studies, compared with the longer period in some temperate mosses, may be an advantage for bryophytes in a savanna environment. 相似文献
16.
大型仪器设备是高校开展教学、科研的物质保证,是高校实验室的主要技术装备,衡量一所高校办学实力和水平的重要指标之一.…… 相似文献
17.
18.
R. Poggioli A. V. Vergoni A. Bertolini 《Cellular and molecular life sciences : CMLS》1985,41(2):265-266
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma. 相似文献
19.
In econometrics, as a rule, the same data set is used to select the model and, conditional on the selected model, to forecast. However, one typically reports the properties of the (conditional) forecast, ignoring the fact that its properties are affected by the model selection (pretesting). This is wrong, and in this paper we show that the error can be substantial. We obtain explicit expressions for this error. To illustrate the theory we consider a regression approach to stock market forecasting, and show that the standard predictions ignoring pretesting are much less robust than naive econometrics might suggest. We also propose a forecast procedure based on the ‘neutral Laplace estimator’, which leads to an improvement over standard model selection procedures. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
20.
Obese postmenopausal female volunteers were given timed daily oral dosages of bromocriptine, and tested for reduction of body fat stores. This dopamine agonist has been shown to reset circadian rhythms that are altered in obese animals and to reduce body fat levels in several animal models. The participants were instructed not to alter their existing exercise and eating behavior during treatment. Skinfold measurements were taken on 33 subjects as indices of body fat. The measurements (e.g., suprailiac) were reduced after six weeks by about 25%, which represents a reduction of 11.7% of the total body fat. These dramatic decreases in body fat, which are equivalent to that produced by severe caloric restriction, were accompanied by more modest reductions of body weight (2.5%), indicating a possible conservation of protein that is usually lost as a consequence of such caloric restriction. The effects of bromocriptine treatment on body fat and hyperglycemia were also examined in non-insulin dependent diabetics being treated with oral hypoglycemics (7 subjects) or insulin (7 subjects). Total body fat was reduced by 10.7% and 5.1% in diabetics on oral hypoglycemics and insulin, respectively, without any significant reductions in body weight. Hyperglycemia was reduced in most of the 15 diabetic subjects treated leading to euglycemia and even cessation of hypoglycemic drugs in 3 of the 7 subjects during 4-8 weeks of bromocriptine treatment. These findings support the hypothesis that obesity and type II diabetes may be treated effectively with bromocriptine when administered at the proper times and dosages. 相似文献