全文获取类型
收费全文 | 6335篇 |
免费 | 17篇 |
国内免费 | 34篇 |
专业分类
系统科学 | 44篇 |
丛书文集 | 58篇 |
教育与普及 | 4篇 |
理论与方法论 | 24篇 |
现状及发展 | 2883篇 |
研究方法 | 356篇 |
综合类 | 2876篇 |
自然研究 | 141篇 |
出版年
2012年 | 105篇 |
2011年 | 252篇 |
2010年 | 36篇 |
2008年 | 147篇 |
2007年 | 169篇 |
2006年 | 155篇 |
2005年 | 146篇 |
2004年 | 142篇 |
2003年 | 126篇 |
2002年 | 145篇 |
2001年 | 175篇 |
2000年 | 211篇 |
1999年 | 124篇 |
1992年 | 109篇 |
1991年 | 79篇 |
1990年 | 87篇 |
1989年 | 80篇 |
1988年 | 67篇 |
1987年 | 85篇 |
1986年 | 89篇 |
1985年 | 137篇 |
1984年 | 89篇 |
1983年 | 79篇 |
1982年 | 67篇 |
1981年 | 70篇 |
1980年 | 77篇 |
1979年 | 149篇 |
1978年 | 145篇 |
1977年 | 152篇 |
1976年 | 136篇 |
1975年 | 154篇 |
1974年 | 168篇 |
1973年 | 128篇 |
1972年 | 121篇 |
1971年 | 183篇 |
1970年 | 270篇 |
1969年 | 167篇 |
1968年 | 166篇 |
1967年 | 187篇 |
1966年 | 146篇 |
1965年 | 97篇 |
1964年 | 56篇 |
1962年 | 38篇 |
1959年 | 68篇 |
1958年 | 83篇 |
1957年 | 81篇 |
1956年 | 53篇 |
1955年 | 48篇 |
1954年 | 55篇 |
1948年 | 42篇 |
排序方式: 共有6386条查询结果,搜索用时 284 毫秒
1.
This paper undertakes a comprehensive examination of 10 measures of core inflation and evaluates which measure produces the best forecast of headline inflation out‐of‐sample. We use the Personal Consumption Expenditure Price Index as our measure of inflation. We use two sets of components (17 and 50) of the Personal Consumption Expenditure Price Index to construct these core inflation measures and evaluate these measures at the three time horizons (6, 12 and 24 months) most relevant for monetary policy decisions. The best measure of core inflation for both sets of components and over all time horizons uses weights based on the first principal component of the disaggregated (component‐level) prices. Interestingly, the results vary by the number of components used; when more components are used the weights based on the persistence of each component is statistically equivalent to the weights generated by the first principal component. However, those forecasts using the persistence of 50 components are statistically worse than those generated using the first principal component of 17 components. The statistical superiority of the principal component method is due to the fact that it extracts (in the first principal component) the common source of variation in the component level prices that accurately describes trend inflation over the next 6–24 months. 相似文献
2.
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
3.
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
4.
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
5.
6.
7.
Summary Acetone and alcohol extracts of the posterior salivary glands ofOctopus vulgaris, Eledone moschata andEledone Aldrovandi contain a principle which strongly reduces the diuresis in hydrated rats.The antidiuretic principle is absent in all otherOctopus tissues as well as in the salivary glands ofOctopus macropus.It shows a high termostability and is strongly adsorbed by animal charcoal at any reaction.The salivary antidiuretic substance is not identical with the posterior pituitary principle nor with the other active substances found in the salivary glands of Octopoda.The injection of salivary extracts satisfactorily reduces polyuria and polydipsia in human diabetes insipidus.
Le presenti ricerche sono state in parte sovvenzionate da un contributo straordinario del Consiglio Nazionale delle Ricerche. 相似文献
Le presenti ricerche sono state in parte sovvenzionate da un contributo straordinario del Consiglio Nazionale delle Ricerche. 相似文献
8.
M. Lazzari V. Franceschini G. Minelli F. Ciani 《Cellular and molecular life sciences : CMLS》1993,49(4):277-281
The corrosion cast technique provided for the first time an excellent three-dimensional visualization of the vascular pattern of the choroid and iris in the newt eye. The results show the presence of a single arterial afference to the choroidal and iris capillaries: the ophthalmic artery is the origin fo both ciliary arteries and the long posterior ciliary artery. Slightly behind the equatorial circumference of the eyeball the venous drainage consists of a single vessel on the dorsal side and two distinct vessels on the ventral one. It receives blood from both iris and choroid. The surface of the plastic endocasts shows some details of fine luminal structures of the endothelial cells. Shallow depressions may be regarded as imprints of endothelial cell nuclei, and they are distinctly different for arteries and capillaries. The angioarchitecture of the newt eye differs from that of brain in that hairpin-shaped capillary loops are not observed at all. 相似文献
9.
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
10.
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