全文获取类型
收费全文 | 36129篇 |
免费 | 719篇 |
国内免费 | 121篇 |
专业分类
系统科学 | 1184篇 |
丛书文集 | 466篇 |
教育与普及 | 40篇 |
理论与方法论 | 358篇 |
现状及发展 | 14428篇 |
研究方法 | 1361篇 |
综合类 | 18650篇 |
自然研究 | 482篇 |
出版年
2018年 | 764篇 |
2017年 | 789篇 |
2016年 | 534篇 |
2012年 | 724篇 |
2011年 | 1865篇 |
2010年 | 991篇 |
2009年 | 584篇 |
2008年 | 1035篇 |
2007年 | 1401篇 |
2006年 | 589篇 |
2005年 | 660篇 |
2004年 | 801篇 |
2003年 | 693篇 |
2002年 | 639篇 |
2001年 | 968篇 |
2000年 | 899篇 |
1999年 | 633篇 |
1992年 | 608篇 |
1991年 | 438篇 |
1990年 | 470篇 |
1989年 | 447篇 |
1988年 | 447篇 |
1987年 | 462篇 |
1986年 | 487篇 |
1985年 | 636篇 |
1984年 | 462篇 |
1983年 | 383篇 |
1982年 | 335篇 |
1981年 | 355篇 |
1980年 | 410篇 |
1979年 | 999篇 |
1978年 | 777篇 |
1977年 | 730篇 |
1976年 | 605篇 |
1975年 | 605篇 |
1974年 | 873篇 |
1973年 | 719篇 |
1972年 | 793篇 |
1971年 | 881篇 |
1970年 | 1211篇 |
1969年 | 945篇 |
1968年 | 839篇 |
1967年 | 842篇 |
1966年 | 804篇 |
1965年 | 598篇 |
1959年 | 299篇 |
1958年 | 576篇 |
1957年 | 404篇 |
1956年 | 314篇 |
1954年 | 333篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
The exponential Radon transform, a generalization of the Radon transform, is defined and studied as a mapping of function
spaces. It is represented in terms of Fourier transform of its domain and range, and this leads to the harmonic decomposition
reconstruction. The results are similar results of Tretiak and Metz.
Foundation item: Supported by the National Natural Science Foundation of China (No. 19971064), Key Project of Science and
Technology of Hubei Province Education Committee.
Biography: Wang Jin-ping (1963-), male, Ph.D. candidate, research direction: numberical solution of singular integral equation
and integral transformation etc. 相似文献
23.
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
24.
YU Jianqiao LIAO Jianwei 《武汉大学学报:自然科学英文版》2007,12(5):887-892
We propose a multiple-tree overlay structure for resource discovery in unstructured P2P systems. Peers that have similar interests or hold similar type of resources will be grouped into a tree-like cluster. We exploit the heterogeneity of peers in each cluster by connecting peers with more capacities closer to the root of the tree. The capacity of a peer can be defined in different ways (e.g. higher network bandwidth, larger disk space, more data items of a certain type etc.) according to different needs of users or applications. 相似文献
25.
In October 1924, The Physical Review, a relatively minor journal at the time, published a remarkable two-part paper by John H. Van Vleck, working in virtual isolation
at the University of Minnesota. Using Bohr’s correspondence principle and Einstein’s quantum theory of radiation along with
advanced techniques from classical mechanics, Van Vleck showed that quantum formulae for emission, absorption, and dispersion
of radiation merge with their classical counterparts in the limit of high quantum numbers. For modern readers Van Vleck’s
paper is much easier to follow than the famous paper by Kramers and Heisenberg on dispersion theory, which covers similar
terrain and is widely credited to have led directly to Heisenberg’s Umdeutung paper. This makes Van Vleck’s paper extremely valuable for the reconstruction of the genesis of matrix mechanics. It also
makes it tempting to ask why Van Vleck did not take the next step and develop matrix mechanics himself.
This paper was written as part of a joint project in the history of quantum physics of the Max Planck Institut für Wissenschaftsgeschichte and the Fritz-Haber-Institut in Berlin. 相似文献
26.
DING Mingtao WEI Fangqiang ZHANG Jinghong WANG Hongjuan 《武汉大学学报:自然科学英文版》2007,12(4):599-604
By analyzing the observation data from Dongchuan Debris Flow Observation and Research Station and historical data from year 1965 to 1990 gotten from National Astronomical Ob-servatories/Yunnan Observatory,the responding of debris flow in Jiangjia Ravine to Solar Proton Flare is studied. The following conclusion can be drawn. Solar Proton Flare,as one of most im-portant astronomical factors,affects the activity of debris flow in Yunnan. Generally,from 1965 to1990,the more active Solar Pro-ton Flare is,the greater the probability of high frequency and large runoff of debris flow is. On the contrary,the less active Solar Pro-ton Flare is,the greater the probability of low frequency,small runoff,and low sediment transport of debris flow is. 相似文献
27.
1 Results This paper presents the development of platinum nanocomposites structures based on organically modified c.a.2 nm core platinum nanoparticles.The chemical modification of the 4-mercaptoaniline functionalized particles by various in coming molecules is evidenced and precisely quantified.The particles can be dissolved like molecules in various solvents depending on the features of the new crown and X-rays shows that the interparticle distance is affected by the crown modification.These platinum n... 相似文献
28.
煤矸石空心砖是一种新型环保墙体材料,符合国家及山西省出台的限制生产和使用实心黏土砖,鼓励发展新型建筑材料的政策。利用煤矸石制造的空心砖可以作为保温材料,既可节约建筑能耗,又可节约土地资源,减少环境污染。煤矸石空心砖同黏土实心砖相比,具有高强、轻质、隔音、隔热、保温、防震等优点,市场前景良好。 相似文献
29.
The unified chaotic system contains the Lorenz system and the Chen system as two dual systems at the two extremes of its parameter
spectrum. This paper presents the design of bang bang controller for unified system and multitude of numerical experiments
under various control parameters. Numerical experiments meet the theoretic proof perfectly and convincingly demonstrated the
controller can be effectively used for unified systems with uncertainty of the equilibrium points. The method enriches the
applications of chaotic control.
Foundation item: Supported by the National Natural Science Foundation of China(50209012)
Biography: Deng Xiao-ming (1980-), male, Master candidate, research direction: chaos control. 相似文献
30.
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