全文获取类型
收费全文 | 6831篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 30篇 |
化学工业 | 320篇 |
金属工艺 | 26篇 |
机械仪表 | 35篇 |
建筑科学 | 118篇 |
矿业工程 | 6篇 |
能源动力 | 48篇 |
轻工业 | 245篇 |
水利工程 | 42篇 |
石油天然气 | 12篇 |
无线电 | 177篇 |
一般工业技术 | 312篇 |
冶金工业 | 5122篇 |
原子能技术 | 25篇 |
自动化技术 | 345篇 |
出版年
2021年 | 17篇 |
2019年 | 22篇 |
2018年 | 22篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 22篇 |
2014年 | 40篇 |
2013年 | 107篇 |
2012年 | 71篇 |
2011年 | 84篇 |
2010年 | 64篇 |
2009年 | 91篇 |
2008年 | 84篇 |
2007年 | 86篇 |
2006年 | 81篇 |
2005年 | 60篇 |
2004年 | 75篇 |
2003年 | 81篇 |
2002年 | 58篇 |
2001年 | 63篇 |
2000年 | 53篇 |
1999年 | 180篇 |
1998年 | 1521篇 |
1997年 | 864篇 |
1996年 | 577篇 |
1995年 | 358篇 |
1994年 | 259篇 |
1993年 | 339篇 |
1992年 | 86篇 |
1991年 | 83篇 |
1990年 | 92篇 |
1989年 | 104篇 |
1988年 | 88篇 |
1987年 | 96篇 |
1986年 | 70篇 |
1985年 | 86篇 |
1984年 | 36篇 |
1983年 | 38篇 |
1982年 | 46篇 |
1981年 | 53篇 |
1980年 | 45篇 |
1979年 | 18篇 |
1978年 | 19篇 |
1977年 | 138篇 |
1976年 | 270篇 |
1975年 | 24篇 |
1974年 | 18篇 |
1973年 | 21篇 |
1972年 | 15篇 |
1970年 | 12篇 |
排序方式: 共有6863条查询结果,搜索用时 31 毫秒
71.
72.
73.
Y Xu DC Gaudette JD Boynton A Frankel XJ Fang A Sharma J Hurteau G Casey A Goodbody A Mellors 《Canadian Metallurgical Quarterly》1995,1(10):1223-1232
Ascites from ovarian cancer patients contain potent growth-promoting activity toward human ovarian cancer cells both in vitro and in vivo. This activity is associated with rapid increases in cytosolic free calcium ([Ca2+]i) as a consequence of phosphoinositide hydrolysis. In this study, we describe the purification, characterization, and identification of an ovarian cancer activating factor (OCAF) from ascites of ovarian cancer patients. We have isolated OCAF by a combination of solvent extraction, silica gel chromatography, and TLC. Mass spectral analysis, phospholipase sensitivity, and gas chromatographic behavior of purified OCAF indicate that OCAF is composed of various species of lysophosphatidic acid (LPA), including LPAs with polyunsaturated fatty acyl chains (linoleic, arachidonic, and docosahexaenoic acids). However, OCAF is more potent than sn-1 palmitoyl, oleoyl, or stearoyl LPA in increasing [Ca2+]i in ovarian cancer cells. The ability of OCAF to alter [Ca2+]i is sensitive to the effects of lipoxidase, whereas the activity of sn-1 oleoyl, stearoyl, or palmitoyl LPA is not, suggesting that polyunsaturated bonds in the fatty acyl chain of OCAF may account for its increased ability to activate ovarian cancer cells. Furthermore, a sn-2 linoleoyl LPA generated by phospholipase A1 treatment of synthetic phosphatidic acid is much more active than are sn-1 palmitoyl, stearoyl, or oleoyl LPA in increasing [Ca2+]i in ovarian cancer cells. Taken together, these data suggest that the ability of OCAF to increase cellular calcium may reside in the structure and/or location of the fatty acyl chain of LPA. Purified OCAF, at concentrations similar to those present in ascites from ovarian cancer patients, was sufficient to induce proliferation of ovarian cancer cells, as indicated by thymidine incorporation, reduction of 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, or colony formation. However, even at optimal concentrations of OCAF, proliferation was lower than that induced by FCS or ascites from ovarian cancer patients, indicating that, although OCAF may be a major regulator of ovarian cancer cells in vivo, it is not the sole mediator present in ascites, and it likely functions in concert with other growth factor activities. 相似文献
74.
75.
76.
W.E. Stewart Jr. A.S. Burns 《International Communications in Heat and Mass Transfer》1992,19(6):859-868
The effects of a permeable inner boundary on the maximum temperature and the convective flows were investigated numerically for a two-dimensional horizontal annulus containing a uniformly heat generating porous media. The time-dependent governing equations were nondimensionalized and put into an explicit finite difference numerical form. The finite difference equations were obtained from truncated Taylor series expansions using a central differencing scheme. Nondimensional temperatures and streamlines were obtained for heat generation rates ranging from 20 to 1,500 W/m3 corresponding to a range of modified Rayleigh numbers of 324 to 24,340 and for several combinations of isothermally heated wall conditions for annuli of radius ratio of 2. It was found that multi-cellular flows occur at the highest Rayleigh numbers investigated. 相似文献
77.
Predicts the future of behavior therapy, focusing on theoretical development, therapeutic techniques, and empirical research. The importance of cognitive and affective processes in behavior change will attract increasing attention. Already one of the most widely adopted approaches, behavior therapy will be used to treat an expanded range of psychiatric disorders and health problems. Research will focus on comparative outcome studies and provide probes for investigating the nature of specific disorders and the mechanisms of therapeutic change. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
79.
HJ Epple FW Kirstein C Bojarski J Frege M Fromm EO Riecken JD Schulzke 《Canadian Metallurgical Quarterly》1997,32(4):308-314
Obliterative or constrictive bronchiolitis is characterized by narrowing of the small airways, due to submucosal and peribronchiolar fibrosis, with chronic obstruction. The vast majority of cases of bronchiolitis obliterans are associated with other diseases and only few cases are idiopathic. We report on the main computed tomography (CT) methods used study obliterative bronchiolitis, the CT findings and the differential diagnosis with other diseases. The dynamic study of alveolar ventilation with CT uses inspiratory and expiratory CT or high-resolution CT (HRCT), spiral dynamic CT or HRCT with advanced image display, ultrafast CT. In abnormal cases HRCT shows direct and indirect signs of small airways disease. The most common (> 80%) sign of obliterative bronchiolitis is the so-called mosaic oligohemia, with low attenuating lobules, caused by air trapping and best seen on expiratory CT, associated with blood flow redistribution to more normal lobules; this finding simulates the ground-glass pattern from infiltrative lung disease. Differential diagnosis is more difficult in the presence of true ground-glass patterns associated with diffuse bronchiolar obstruction and also with mosaic oligohemia due to pulmonary vascular disease and pulmonary emphysema. HRCT can distinguish these diseases and dynamic CT is more sensitive than functional tests in detecting regional abnormalities and air trapping. The combination of HRCT, rapid volumetric scanning and advanced image display is a powerful tool study the normal and abnormal features of bronchiolar function and alveolar ventilation. 相似文献
80.
S Uribe-Luna JD Quintana-Hau R Maldonado-Rodriguez M Espinosa-Lara KL Beattie D Farquhar JA Nelson 《Canadian Metallurgical Quarterly》1997,54(3):419-424
The stimulatory effect of phytin added to skim milk on acid production of Lactobacillus casei was examined. Phytin stimulated acid production of L. casei fairly well. The stimulatory effect of phytin on acid production was not shown when phytin was treated with Dowex 50 (H+) and neutralized by NaOH solution. The incinerated product of phytin maintained almost equal stimulatory effect on acid production as that before processing. The addition of Mn2+ in the amount contained in a reagent phytin augmented the stimulatory effect on acid production markedly. The further addition of Fe3+, Ca2+, Mg2+ and PO4(3-) in amounts corresponding to their contents in the preparation of phytin as well as Mn2+ increased the effect slightly. The four preparations of phytin contained 0.045-0.20% of Mn, and the greater the Mn content was, the greater the potentiation of acid production. 相似文献