全文获取类型
收费全文 | 25239篇 |
免费 | 2123篇 |
国内免费 | 928篇 |
学科分类
工业技术 | 28290篇 |
出版年
2024年 | 52篇 |
2023年 | 424篇 |
2022年 | 601篇 |
2021年 | 1089篇 |
2020年 | 862篇 |
2019年 | 714篇 |
2018年 | 821篇 |
2017年 | 826篇 |
2016年 | 774篇 |
2015年 | 958篇 |
2014年 | 1241篇 |
2013年 | 1532篇 |
2012年 | 1538篇 |
2011年 | 1629篇 |
2010年 | 1392篇 |
2009年 | 1257篇 |
2008年 | 1235篇 |
2007年 | 1215篇 |
2006年 | 1121篇 |
2005年 | 911篇 |
2004年 | 697篇 |
2003年 | 706篇 |
2002年 | 811篇 |
2001年 | 648篇 |
2000年 | 537篇 |
1999年 | 563篇 |
1998年 | 823篇 |
1997年 | 599篇 |
1996年 | 484篇 |
1995年 | 323篇 |
1994年 | 305篇 |
1993年 | 240篇 |
1992年 | 176篇 |
1991年 | 160篇 |
1990年 | 126篇 |
1989年 | 122篇 |
1988年 | 82篇 |
1987年 | 62篇 |
1986年 | 73篇 |
1985年 | 55篇 |
1984年 | 53篇 |
1983年 | 46篇 |
1982年 | 46篇 |
1981年 | 40篇 |
1980年 | 42篇 |
1979年 | 27篇 |
1977年 | 46篇 |
1976年 | 70篇 |
1975年 | 18篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
61.
62.
To prevent post-transfusional hepatitis B and C, two epidemiologic studies were performed. The first, based on the frequencies distribution of hepatitis B virus serological markers versus sex and classes of age, has permitted the assessment of the profile of the infection in a population composed of 573 north vietnamese blood donors. There is no significant difference between men and women frequencies of HBs antigen (11.5%), anti-HBs antibody (70.2%) and anti-HBc antibody alone (3.8%), but a significant difference of no-marker frequencies: 7.8% and 17.9% in men and women respectively (X2 = 9.11; p = 0.010). The percentage of no-marker decreases when the mean age of each class increases. The second, using the increase of the serum alanine aminotransferase (ALAT) activity as an indirect marker of non-A, non-B hepatitis for determining in a population of more than 25,000 parisian blood donors, the percentage of donors eliminated. They are between 0.70 and 0.76 in women and 2.26 and 2.46 in men. These investigations can be applied to prevent the hepatitis B transmission in a population of 102 south vietnamese women in age to procreate or to determine the percentage of blood donors eliminated (3.12%) in a population of 2,950 Parisians composed in majority (50.9%) of new donors. The hemobiologist will have an important role to elaborate strategies for orientation of blood gifts with hepatitis B and C virus markers. 相似文献
63.
F Douaud N Le Roch J Renault R Havouis M Vaultier JP Moulinoux N Seiler 《Canadian Metallurgical Quarterly》1997,12(8):621-633
Several dimethylsilane tetramines [homologs of spermine with an Si(CH3)2 group in the central carbon chain], a carbon analog of the dimethylsilane tetramines [containing C(CH3)2 instead of Si(CH3)2] and a dimethylsilane hexamine were studied with regard to their cytotoxic activity and their ability to interact with double-stranded DNA. All polyamine analogs exerted cytostatic effects to several cell lines at micromolar concentrations. Their ability to condense DNA was comparable to and their ability to displace ethidium bromide from binding to DNA was superior to that of spermine. Their cytostatic effect was not correlated with the depletion of cellular spermidine concentrations. It is suggested that the new polyamine analogs act mainly by displacing spermidine from binding sites which are essential for the promotion of cell growth. 相似文献
64.
Le C.T.C. Ishimaru A. Kuga Y. Yea J.-H. 《Geoscience and Remote Sensing, IEEE Transactions on》1998,36(1):61-71
The polarimetric angular memory effect is applied to obtain the average topographic height of a rough surface. This novel effect improves the height sensitivity while maintaining a good degree of correlation between the sensors. By using a reference flat surface, the interferometric phase is linearly related to the mean topographic height. The combination of angular memory and wideband frequency interferometry (AMFI) is realized and offers a means to design a robust interferometric system. Extension of the technique to the pulse scattering problem is studied through the two-frequency mutual coherence function, and its time-domain transform provides an equivalent way to obtain the mean topographic height by combining both spatial and temporal diversity. Millimeter-wave (MMW) experiments are conducted with rough surfaces of different statistics and scattering media of different types (gravel, sand, and rough surfaces) to prove the effectiveness of the technique 相似文献
65.
On the magnetic-wall approximation for their slots, shielded coplanar waveguides (SCPWs) and semienclosed CPWs (SECPWs) are analyzed through an intensive use of elliptic function transformation. CAD-oriented formulas for the quasi-TEM parameters of SCPWs and SECPWs, including their coupled versions, are derived. The comparison of the results calculated here with previous ones show 2% accuracy for formulas in the practical situation where the slots are not too wide, e.g., s / (s + 2w) ≥ 0.2 for an SCPW. © 1994 John Wiley & Sons, Inc. 相似文献
66.
工业过程随机稳态优化控制算法的鲁棒性分析 总被引:1,自引:0,他引:1
本文给出了一种随机稳态优化算法的灵敏度分析,讨论算法解对参数变化的关系。这些参数代表系统结构参数或噪声向量的某些数字特征. 相似文献
67.
68.
69.
采用晶种技术,能有效地改善熟料的煅烧过程和熟料的质量。晶种和复合矿化剂的作用机理不同,在某些方面具有互补性。 相似文献
70.