首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2681篇
  免费   84篇
  国内免费   8篇
电工技术   155篇
综合类   7篇
化学工业   831篇
金属工艺   95篇
机械仪表   68篇
建筑科学   53篇
能源动力   137篇
轻工业   203篇
水利工程   2篇
石油天然气   2篇
无线电   187篇
一般工业技术   442篇
冶金工业   296篇
原子能技术   64篇
自动化技术   231篇
  2023年   20篇
  2022年   54篇
  2021年   81篇
  2020年   34篇
  2019年   26篇
  2018年   41篇
  2017年   51篇
  2016年   68篇
  2015年   38篇
  2014年   79篇
  2013年   172篇
  2012年   115篇
  2011年   162篇
  2010年   121篇
  2009年   165篇
  2008年   138篇
  2007年   119篇
  2006年   101篇
  2005年   111篇
  2004年   90篇
  2003年   88篇
  2002年   68篇
  2001年   38篇
  2000年   49篇
  1999年   53篇
  1998年   133篇
  1997年   92篇
  1996年   76篇
  1995年   60篇
  1994年   53篇
  1993年   49篇
  1992年   17篇
  1991年   23篇
  1990年   21篇
  1989年   19篇
  1988年   15篇
  1987年   12篇
  1986年   12篇
  1985年   15篇
  1984年   11篇
  1983年   9篇
  1982年   8篇
  1981年   11篇
  1980年   8篇
  1979年   4篇
  1977年   9篇
  1976年   10篇
  1975年   3篇
  1973年   5篇
  1972年   4篇
排序方式: 共有2773条查询结果,搜索用时 0 毫秒
21.
Differentiation of endometrial stromal cells (decidualization) is essential for embryo implantation and maintenance of pregnancy. By sequential complementary DNA subtractive hybridization, one of the messenger RNAs (mRNA) induced by progesterone in human endometrial stromal cells decidualized in vitro was identified as that of a tissue transglutaminase type II (TGase). TGase mRNA was induced within 6 h after the addition of progesterone to the culture, and the effect was dose dependent. Both the TGase inhibitor monodansylcadaverine and oligodeoxynucleotide complementary to the TGase mRNA inhibited the decidualization, as assessed by PRL production and morphological transformation. Expression of TGase mRNA in human decidua and endometria exposed to high levels of progesterone in vivo was demonstrated by Northern blotting and in situ hybridization. These data suggest that TGase is necessary for the decidualization of human endometrial stromal cells and that clarification of the mechanism of action of TGase will facilitate further insight into the diagnosis and treatment of infertility.  相似文献   
22.
Serum p53 protein levels were measured in 36 patients with small cell lung cancer (SCLC) and 35 patients with benign lung diseases in order to evaluate the relationship of these levels to clinicopathological features of SCLC. Serum levels of p53 protein were measured by an enzyme-linked immunosorbent assay, p53 protein level was 23.92 +/- 6.78 pg/ml in patients with SCLC, and similar to that (17.47 +/- 2.86 pg/ml) in patients with benign lung diseases. By the clinical stage of SCLC, the mean level of p53 protein was 16.68 +/- 4.62 pg/ml in 21 patients with limited disease, and lower than that in 15 patients with extensive disease (34.05 +/- 14.84 pg/ml) (P = 0.23). The levels of p53 protein were not correlated with age, smoking index, or presence of cancer history for patients with SCLC. However, immunohistochemical examination disclosed a mild correlation between the expression of p53 protein by SCLC tumor and p53 protein serum level (r = 0.45, P = 0.02). Two patients with SCLC had an elevated serum level of p53 protein (> 2 S.D. above the mean for benign lung diseases). However, measurement of p53 protein serum level was not found to be clinically useful for detection of SCLC.  相似文献   
23.
24.
The setup and deposition conditions of electrode arrangement and pressure have been studied to synthesize diamond films at high growth rate on wide area efficiently by arc discharge plasma jet chemical vapor deposition. An apparatus has been used in which four plasma torches, one is used for cathode and the others for divided anodes, are arranged and the positions of these torches are changeable. Growth rate, deposition area and thickness of diamond films have increased with changing the electrode arrangements without improvement of thickness variation. Maximum growth rate of our apparatus has occurred at the pressure of 6.7 kPa and diamond films that have less variations of quality and surface roughness have been synthesized at lower pressure during deposition. Moreover, a high conversion rate, which is the ratio of carbon atoms that form diamond in supplied methane gas, of 16% has been obtained at the pressure of 6.7 kPa and methane concentration of 2%.  相似文献   
25.
Crystals of yttria partially stabilized zirconia were grown by the arc-image floating-zone technique and studied by transmission electron microscopy. Crystals annealed at 1700°C consist of tetragonal precipitates and a cubic matrix. The platelike domains in a precipitate are twin-related tetragonal variants stacked alternately parallel to the (011) twin plane. The axial relations between the tetragonal precipitate and the cubic matrix are [100]tetragonal|[100]cubic, [011]tetragonal|[011]cubic.  相似文献   
26.
Tensile tests of a 17Cr-7Ni-1Al steel were carried out at 0.1, 300 and 600 MPa hydrostatic pressure, and the mechanical properties of the material were found to be considerably changed by the pressure. The martensitic transition temperatureM s decreased under pressure. The volume fraction of-martensite induced by tensile deformation increased with strain, but was suppressed by hydrostatic pressure. The yield stress increased with pressure. The yield surface became a nonlinear cone with a pointed apex. The stress-strain curve was considerably changed by pressure, and was expressed by a modified identical-strain model (law of mixture) as a quantitative function. Uniform-strain limit increased with pressure. It was found that these changes were not caused by the mechanical effect of hydrostatic pressure, but by its thermodynamic effects.  相似文献   
27.
Electrical conductivity of two types of lanthanum-doped barium titanote ceramics with different dopant levels was measured at temperatures between 900 and 1250° C andP O 2from 10–5 to 1 atm. The activation energies of the conduction for the two are interpreted in terms of the formation energy of ionized oxygen vacancies even in such a highP O 2region. This fact is in contrast with a well -known controlled -valency model proposed for rare- earth -doped semi-conducting perovskites. In a lightly lanthanum-doped specimen, semiconduction achieved at elevated temperatures is retained on cooling the specimen to room temperature, whereas in a heavily doped specimen, the resultant high-temperature semiconduction changed to insulation on cooling. The former behaviour on cooling is successfully explained by a metastabilization of oxygen vacancies accompanied by electrons formed at elevated temperatures.  相似文献   
28.
Ethane, ethene, ethyne and hydrogen are obtained in good yields via dehydrogenative coupling of methane in the presence of active carbon as a catalyst. The product yield is increased by supporting metal on active carbon.  相似文献   
29.
The levels of phosphatidylcholine hydroperoxide in serially cultured human fetal diploid fibroblasts at various population doubling levels were determined by high-performance liquid chromatography combined with chemiluminescence detections. This methodology utilizes a mixture of cytochromec and luminol as post-column hydroperoxide group specific luminescent reagents. The cellular hydroperoxide content increased with age from 0.34 to 27.72 pmol/106 cells. At the end of the cells'in vitro lifespan (51st population doubling level), the hydroperoxide content per 106 cells reached about 80 times the level found in cells of the 20th population doubling level. Supplementation of exogenous α-tocopherol to the culture medium prevented hydroperoxide accumulation, but did not extent the lifespanin vitro. The results indicate that substantial intracellular phospholipid hydroperoxide accumulation occurred in the course of aging of human fetal liploid fibroblasts.  相似文献   
30.
We report fast computation of computer-generated holograms (CGHs) using Xeon Phi coprocessors, which have massively x86-based processors on one chip, recently released by Intel. CGHs can generate arbitrary light wavefronts, and therefore, are promising technology for many applications: for example, three-dimensional displays, diffractive optical elements, and the generation of arbitrary beams. CGHs incur enormous computational cost. In this paper, we describe the implementations of several CGH generating algorithms on the Xeon Phi, and the comparisons in terms of the performance and the ease of programming between the Xeon Phi, a CPU and graphics processing unit (GPU).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号