全文获取类型
收费全文 | 12290篇 |
免费 | 34篇 |
国内免费 | 49篇 |
专业分类
系统科学 | 42篇 |
丛书文集 | 90篇 |
教育与普及 | 31篇 |
理论与方法论 | 44篇 |
现状及发展 | 5195篇 |
研究方法 | 584篇 |
综合类 | 6230篇 |
自然研究 | 157篇 |
出版年
2013年 | 116篇 |
2012年 | 211篇 |
2011年 | 354篇 |
2010年 | 94篇 |
2009年 | 76篇 |
2008年 | 209篇 |
2007年 | 245篇 |
2006年 | 229篇 |
2005年 | 238篇 |
2004年 | 226篇 |
2003年 | 229篇 |
2002年 | 213篇 |
2001年 | 398篇 |
2000年 | 374篇 |
1999年 | 281篇 |
1992年 | 236篇 |
1991年 | 183篇 |
1990年 | 208篇 |
1989年 | 194篇 |
1988年 | 205篇 |
1987年 | 211篇 |
1986年 | 163篇 |
1985年 | 250篇 |
1984年 | 170篇 |
1983年 | 150篇 |
1982年 | 166篇 |
1981年 | 137篇 |
1980年 | 176篇 |
1979年 | 387篇 |
1978年 | 295篇 |
1977年 | 289篇 |
1976年 | 253篇 |
1975年 | 290篇 |
1974年 | 311篇 |
1973年 | 311篇 |
1972年 | 344篇 |
1971年 | 346篇 |
1970年 | 430篇 |
1969年 | 363篇 |
1968年 | 381篇 |
1967年 | 354篇 |
1966年 | 320篇 |
1965年 | 204篇 |
1959年 | 107篇 |
1958年 | 204篇 |
1957年 | 138篇 |
1956年 | 122篇 |
1955年 | 105篇 |
1954年 | 81篇 |
1948年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
从“十四五”保护与发展的生态关系角度,探讨了生态保护与绿色发展的十大生态关系,阐述了生态保护和绿色发展中的一系列有关生态关系的生态智慧及生态技术,并对长江、黄河等流域的生态保护和修复提出了相关建议。 相似文献
2.
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
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.
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.
6.
7.
8.
9.
Although theoretical studies show that overcompensatory density-dependent mechanisms can potentially generate regular or chaotic fluctuations in animal numbers, the majority of realistic single-species models of invertebrate populations are not overcompensatory enough to cause sustained population cycles. The possibility that overcompensation may generate cycles or chaos in vertebrate populations has seldom been considered. Here we show that highly overcompensatng density-dependent mortality can generate recurrent population crashes consistent with those observed in a naturally limited population of Soay sheep. The observed interval of three or more years between crashes points to sharp 'focusing' of mortality over a narrow range of population density. 相似文献
10.
Shiga toxin and some other protein toxins that act on targets in the cytosol have previously been shown to enter the trans-Golgi network. Transport by this route may be necessary for translocation of the toxin to the cytosol and for intoxication, but it is not known whether the enzymatically active part of the toxins actually enters the cytosol from the trans-Golgi network. It has been suggested that such toxins are transported in a retrograde manner to the endoplasmic reticulum and that translocation occurs in this organelle, but retrograde transport of endocytosed material beyond the trans-Golgi network has never been demonstrated. Here we show that in butyric acid-treated A431 cells endocytosed Shiga toxin is not only transported to the trans-Golgi network, but also to all Golgi stacks, to the endoplasmic reticulum and to the nuclear envelope. Furthermore, butyric acid sensitizes the cells to Shiga toxin, which is consistent with the possibility that retrograde transport is required for translocation of the toxin to the cytosol. 相似文献