全文获取类型
收费全文 | 5779篇 |
免费 | 27篇 |
国内免费 | 38篇 |
专业分类
系统科学 | 38篇 |
丛书文集 | 67篇 |
教育与普及 | 5篇 |
理论与方法论 | 21篇 |
现状及发展 | 2699篇 |
研究方法 | 285篇 |
综合类 | 2659篇 |
自然研究 | 70篇 |
出版年
2017年 | 42篇 |
2013年 | 42篇 |
2012年 | 102篇 |
2011年 | 176篇 |
2009年 | 46篇 |
2008年 | 128篇 |
2007年 | 155篇 |
2006年 | 143篇 |
2005年 | 120篇 |
2004年 | 129篇 |
2003年 | 114篇 |
2002年 | 129篇 |
2001年 | 174篇 |
2000年 | 186篇 |
1999年 | 123篇 |
1992年 | 95篇 |
1991年 | 74篇 |
1990年 | 75篇 |
1989年 | 68篇 |
1988年 | 55篇 |
1987年 | 76篇 |
1986年 | 73篇 |
1985年 | 129篇 |
1984年 | 76篇 |
1983年 | 69篇 |
1982年 | 60篇 |
1981年 | 63篇 |
1980年 | 74篇 |
1979年 | 139篇 |
1978年 | 128篇 |
1977年 | 136篇 |
1976年 | 126篇 |
1975年 | 137篇 |
1974年 | 149篇 |
1973年 | 114篇 |
1972年 | 102篇 |
1971年 | 151篇 |
1970年 | 231篇 |
1969年 | 154篇 |
1968年 | 138篇 |
1967年 | 166篇 |
1966年 | 125篇 |
1965年 | 83篇 |
1964年 | 48篇 |
1959年 | 67篇 |
1958年 | 82篇 |
1957年 | 82篇 |
1956年 | 52篇 |
1955年 | 48篇 |
1954年 | 54篇 |
排序方式: 共有5844条查询结果,搜索用时 671 毫秒
1.
随着城市化高速发展,老厂房再利用的问题日益急迫.上海是中国近代工业起源地,也是率先着手对彰显城市文脉的工业遗产进行调查和保护的历史文化名城.本文以上海典型案例入手,分析了具有代表性的老厂房改造的项目特点,并在此基础上,对常州大成三厂这一民国时期的纺织业遗留地块进行改造设计手法进行介绍,从设计理念、设计内容和节点设计3个方面,体现了文化传承和生态技术相融合理念. 相似文献
2.
Online auctions have become increasingly popular in recent years. There is a growing body of research on this topic, whereas modeling online auction price curves constitutes one of the most interesting problems. Most research treats price curves as deterministic functions, which ignores the random effects of external and internal factors. To account for the randomness, a more realistic model using stochastic differential equations is proposed in this paper. The online auction price is modeled by a stochastic differential equation in which the deterministic part is equivalent to the second‐order differential equation model proposed in Wang et al. (Journal of the American Statistical Association, 2008, 103, 1100–1118). The model also includes a component representing the measurement errors. Explicit expressions for the likelihood function are also obtained, from which statistical inference can be conducted. Forecast accuracy of the proposed model is compared with the ODE (ordinary differential equation) approach. Simulation results show that the proposed model performs better. 相似文献
3.
In recent years there has been a growing interest in exploiting potential forecast gains from the non‐linear structure of self‐exciting threshold autoregressive (SETAR) models. Statistical tests have been proposed in the literature to help analysts check for the presence of SETAR‐type non‐linearities in an observed time series. It is important to study the power and robustness properties of these tests since erroneous test results might lead to misspecified prediction problems. In this paper we investigate the robustness properties of several commonly used non‐linearity tests. Both the robustness with respect to outlying observations and the robustness with respect to model specification are considered. The power comparison of these testing procedures is carried out using Monte Carlo simulation. The results indicate that all of the existing tests are not robust to outliers and model misspecification. Finally, an empirical application applies the statistical tests to stock market returns of the four little dragons (Hong Kong, South Korea, Singapore and Taiwan) in East Asia. The non‐linearity tests fail to provide consistent conclusions most of the time. The results in this article stress the need for a more robust test for SETAR‐type non‐linearity in time series analysis and forecasting. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
4.
复数,实数及实对称数据下Bruun FFT算法的实现 总被引:3,自引:0,他引:3
本文在复数、实数以及实对称数据下研究和实现了Bruun FFT算法。文章分析和评价了各种数据下BruunFFT的运算量和特点,提出了算法的实现结构和方法。最后给了TMS320C30上的运算时间,我们实现的算法比基2FFT速度提高35%。 相似文献
5.
6.
F. Weygand A. Wacker V. Schmied-Kowarzik 《Cellular and molecular life sciences : CMLS》1948,4(11):427-428
Summary By condensing 2:4:5-triamino-6-hydroxy-pyrimidine with dihydroxyacetone (diacetate), diaminoacetone or acetone-1,3-di (p-formylaminobenzoic acid) not the expected 8- or 9-oxymethyl resp. -aminomethyl-pteridines but 8-or 9-methyl-pteridines were obtained. With p-tolyl-d-isoglucosamine not a tetrahydroxybutyl-pteridine but a trihydroxybutyl-pteridine was formed. For an explanation of these results it is supposed that from the dihydro-pteridines formed at first by intramolecular splitting off of H2O or R·NH2 aromatization takes place. 相似文献
7.
V.A.帕瑟根 《国外科技新书评介》2007,(2):7-7
分子间的范德华力是十分微弱的,但可以说普遍的存在着,在很多体系中起着巨大的作用,在物理学、化学、生物学等学科中得到了广泛的研究。但怎样计算范德华力?如何考虑各种条件对范德华力的影响? 相似文献
8.
9.
Association scan of 14,500 nonsynonymous SNPs in four diseases identifies autoimmunity variants 总被引:2,自引:0,他引:2
Wellcome Trust Case Control Consortium;Australo-Anglo-American Spondylitis Consortium 《Nature genetics》2007,39(11):1329-1337
We have genotyped 14,436 nonsynonymous SNPs (nsSNPs) and 897 major histocompatibility complex (MHC) tag SNPs from 1,000 independent cases of ankylosing spondylitis (AS), autoimmune thyroid disease (AITD), multiple sclerosis (MS) and breast cancer (BC). Comparing these data against a common control dataset derived from 1,500 randomly selected healthy British individuals, we report initial association and independent replication in a North American sample of two new loci related to ankylosing spondylitis, ARTS1 and IL23R, and confirmation of the previously reported association of AITD with TSHR and FCRL3. These findings, enabled in part by increased statistical power resulting from the expansion of the control reference group to include individuals from the other disease groups, highlight notable new possibilities for autoimmune regulation and suggest that IL23R may be a common susceptibility factor for the major 'seronegative' diseases. 相似文献
10.