全文获取类型
收费全文 | 8044篇 |
免费 | 672篇 |
国内免费 | 466篇 |
专业分类
电工技术 | 558篇 |
综合类 | 582篇 |
化学工业 | 897篇 |
金属工艺 | 400篇 |
机械仪表 | 547篇 |
建筑科学 | 571篇 |
矿业工程 | 160篇 |
能源动力 | 171篇 |
轻工业 | 1117篇 |
水利工程 | 282篇 |
石油天然气 | 126篇 |
武器工业 | 62篇 |
无线电 | 688篇 |
一般工业技术 | 641篇 |
冶金工业 | 1219篇 |
原子能技术 | 90篇 |
自动化技术 | 1071篇 |
出版年
2024年 | 36篇 |
2023年 | 108篇 |
2022年 | 205篇 |
2021年 | 350篇 |
2020年 | 209篇 |
2019年 | 140篇 |
2018年 | 173篇 |
2017年 | 183篇 |
2016年 | 180篇 |
2015年 | 291篇 |
2014年 | 371篇 |
2013年 | 482篇 |
2012年 | 513篇 |
2011年 | 539篇 |
2010年 | 558篇 |
2009年 | 509篇 |
2008年 | 535篇 |
2007年 | 517篇 |
2006年 | 472篇 |
2005年 | 397篇 |
2004年 | 274篇 |
2003年 | 189篇 |
2002年 | 158篇 |
2001年 | 172篇 |
2000年 | 155篇 |
1999年 | 95篇 |
1998年 | 334篇 |
1997年 | 207篇 |
1996年 | 139篇 |
1995年 | 78篇 |
1994年 | 77篇 |
1993年 | 66篇 |
1992年 | 35篇 |
1991年 | 47篇 |
1990年 | 38篇 |
1989年 | 38篇 |
1988年 | 31篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 22篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1977年 | 30篇 |
1976年 | 54篇 |
1975年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有9182条查询结果,搜索用时 31 毫秒
991.
992.
993.
994.
995.
996.
J Tongio F Mantz JJ Wenger P Warter R Kiény G Foucher C Chemorin P Bareiss MO Spach 《Canadian Metallurgical Quarterly》1976,57(6-7):521-525
The authors describe two cases of secreting paragangliomas of the organ of Zuckerkandl, beinging the number of known cases to 78. They underline the interest of arteriographic and phlebographic explorations which define more accurately the origin and spread of these tumours. 相似文献
997.
J. W. Nielsen S. L. Blank D. H. Smith G. P. Vella-Coleiro F. B. Hagedorn R. L. Barns W. A. Biolsi 《Journal of Electronic Materials》1974,3(3):693-707
The choice of magnetic garnet compositions for bubble memories is always a compromise dictated by the material requirements
generated by the specifications on the memories. The three compositions reported, Y2.62Smo.38Fe3.85Ga1.15O12, Gd2.lLuO.9Fe4.4Al0.6O12, and Yl.92Sm0.1Ca0.98Fe4.02Ge0.98O12, represent three examples of such a compromise. The first composition is excellent for use in circuits operating at 100 KHz over a temperature range of -20° to 80°C. The second has a mobility up to 5000 cm/sec/0e and is capable of very high speed
operation at the sacrifice of stability toward temperature. The third exhibits excellent stability toward temperature and
has operated at 1 MHz but is compositionally more complex.
Melt compositions for film growth and a summary of magnetic properties are presented for the three compositions. Factors to
be weighed in composition selection for bubble domain memories are discussed. 相似文献
998.
A sensitive method based on ferrocene-streptavidin (Fc-Stv) conjugates for the simultaneously amplified electrochemical and surface plasmon optical detection of DNA target hybridization to peptide nucleic acid-modified gold surfaces is reported. The attachment of Fc-Stv to the biotinylated complementary target DNA not only amplified the surface plasmon resonance signal but also enhanced the electrochemical signal due to the many Fc markers per Stv. The ferrocene redox peak current increased with the increase of the target DNA concentration. Consequently, the amount of hybridized target DNA can be estimated by cyclic voltammetry and chronocoulometry. The detection limit of this DNA sensor is 10 pM (2 fmol, with signal to noise > 3). This sensor was also shown to have high selectivity (at the single-base mismatch level) and good reproducibility. 相似文献
999.
Hammer NA Hansen Tv Byskov AG Rajpert-De Meyts E Grøndahl ML Bredkjaer HE Wewer UM Christiansen J Nielsen FC 《Reproduction (Cambridge, England)》2005,130(2):203-212
Insulin-like growth factor-II mRNA-binding proteins 1, 2 and 3 (IMP1, IMP2 and IMP3) belong to a family of RNA-binding proteins implicated in mRNA localization, turnover and translational control. We examined their expression pattern during development of murine and human testis and ovaries. In the mouse, IMPs were expressed in male and female gonadal cells at embryonic day 12.5 (E12.5). From E16.5, IMP1 and IMP3 became restricted to the developing germ cells, whereas IMP2 expression persisted in the interstitial cells. In mature mouse and human ovaries, IMP1, IMP2 and IMP3 were detected in resting and growing oocytes and in the granulosa cells. In testis, IMP1 and IMP3 were found mainly in the spermatogonia, whereas IMP2 was expressed in the immature Leydig cells. Moreover, all three IMPs were detected in human semen. The developmental expression pattern of IMP1 and IMP3 in the human testis prompted us to examine their possible involvement in testicular neoplasia. IMPs were detected primarily in germ-cell neoplasms, including preinvasive testicular carcinoma in situ, classical and spermatocytic seminoma, and nonseminomas, with particularly high expression in undifferentiated embryonal carcinoma. The relative expression of IMP1, IMP2 and IMP3 varied among tumor types and only IMP1 was detected in all carcinoma in situ cells. Thus IMPs, and in particular IMP1, may be useful auxiliary markers of testicular neoplasia. 相似文献
1000.
Dorte?Krause-JensenEmail author Tina?Maria?Greve Kurt?Nielsen 《Water Resources Management》2005,19(1):63-75
Eelgrass is the most widespread plant in temperate coastal waters. It is regarded as a useful indicator of water quality because water clarity regulates its extension towards deeper waters, i.e. the depth limit. This study analyses the use of eelgrass depth limits as a bioindicator under the Water Framework Directive (WFD). The WFD demands that ecological status is classified by relating the actual level of bioindicators to a so-called reference level, reflecting a situation of limited anthropogenic influence. The directive further demands that reference levels are defined for water body types with similar hydromorphological characteristics, and that the classification thereby becomes type-specific.A large historic data set on depth limits of eelgrass around 1900 was used to characterise reference levels, and a large data set from the Danish National Monitoring and Assessment Programme to characterise actual depth limits. Data represented a wide range of Danish coastal water bodies that were grouped into 10 water body types based on differences in salinity and water depth.The analyses clearly illustrate that the definition of ecological status classes markedly influence the assessment of ecological status according to the WFD. Moreover, the study demonstrates that the use of type-specific classification implies a risk of misinterpreting ecological status. Classification problems were pronounced in spite of a unique data material on reference conditions, and the problems are likely to be even greater in cases where reference conditions are less well defined. A more robust classification was obtained by using reference levels for individual sites in a site-specific classification.In conclusion, when classifying water quality on the basis of eelgrass depth limits, site-specific reference levels are recommended if such data are available. If more general information on reference levels is used, local conditions known to affect depth limits must be taken into account. 相似文献