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   34667篇
  免费   1065篇
  国内免费   110篇
电工技术   375篇
综合类   228篇
化学工业   5058篇
金属工艺   622篇
机械仪表   581篇
建筑科学   967篇
矿业工程   93篇
能源动力   929篇
轻工业   3842篇
水利工程   241篇
石油天然气   151篇
武器工业   6篇
无线电   2236篇
一般工业技术   4084篇
冶金工业   12475篇
原子能技术   237篇
自动化技术   3717篇
  2024年   50篇
  2023年   150篇
  2022年   491篇
  2021年   781篇
  2020年   530篇
  2019年   597篇
  2018年   683篇
  2017年   765篇
  2016年   716篇
  2015年   550篇
  2014年   848篇
  2013年   1398篇
  2012年   1244篇
  2011年   1572篇
  2010年   1148篇
  2009年   1198篇
  2008年   1090篇
  2007年   957篇
  2006年   769篇
  2005年   832篇
  2004年   899篇
  2003年   816篇
  2002年   785篇
  2001年   691篇
  2000年   539篇
  1999年   676篇
  1998年   3875篇
  1997年   2417篇
  1996年   1649篇
  1995年   974篇
  1994年   808篇
  1993年   903篇
  1992年   264篇
  1991年   377篇
  1990年   327篇
  1989年   276篇
  1988年   304篇
  1987年   243篇
  1986年   239篇
  1985年   236篇
  1984年   128篇
  1983年   102篇
  1982年   146篇
  1981年   166篇
  1980年   168篇
  1979年   90篇
  1978年   98篇
  1977年   312篇
  1976年   570篇
  1975年   92篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Physalis angulata L (Solanaceae) is a medicinal plant from North of Brazil, whose different extracts and infusions are commonly used in the popular medicine for the treatment of malaria, asthma, hepatitis, dermatitis and rheumatism. However, the genotoxic effects of P. angulata on human cells is not well known. The main purpose of the present study was to evaluate the in vitro genotoxic effects of aqueous extract of P. angulata using the comet assay and the micronucleus assay in human lymphocytes provided from 6 healthy donors. Treatments with P. angulata extracts were performed in vitro in order to access the extent of DNA damage. The comet assay has shown that treatments with P. angulata at 0.5, 1.0, 2.0, 3.0 and 6.0 microg/mL in culture medium were genotoxic. Lymphocytes treated with P. angulata at the concentrations of 3.0 and 6.0 microg/mL in culture medium showed a statistically significant increase in the frequency of micronucleus (p<0.05), however, the cytokinesis blocked proliferation index (CBPI) was not decreased after P. angulata treatment. In conclusion, the present work demonstrated the genotoxic effects of P. angulata extract on human lymphocytes in vitro.  相似文献   
52.
BACKGROUND: Nisin is a commercially available bacteriocin produced by Lactococcus lactis ATCC 11454 and used as a natural agent in the biopreservation of food. In the current investigation, milk whey, a byproduct from dairy industries was used as a fermentation substrate for the production of nisin. Lactococcus lactis ATCC 11454 was developed in a rotary shaker (30 °C/36 h/100 rpm) using two different media with milk whey (i) without filtration, pH 6.8, adjusted with NaOH 2 mol L?1 and without pH adjustment, both autoclaved at 121 °C for 30 min, and (ii) filtrated (1.20 µm and 0.22 µm membrane filter). These cultures were transferred five times using 5 mL aliquots of broth culture for every new volume of the respective media. RESULTS: The results showed that culture media composed of milk whey without filtration supplied L. lactis its adaptation needs better than filtrated milk whey. Nisin titers, in milk whey without filtration (pH adjusted), was 11120.13 mg L?1 in the second transfer, and up to 1628‐fold higher than the filtrated milk whey, 6.83 mg.L?1 obtained in the firstt transfer. CONCLUSIONS: Biological processing of milk byproducts (milk whey) can be considered a profitable alternative, generating high‐value bioproducts and contributing to decreasing river disposals by dairy industries. Copyright © 2008 Society of Chemical Industry  相似文献   
53.
54.
55.
Sera from 82 cases of leptospirosis (confirmed by micro-agglutination tests or IFAT) and 108 patients with other diseases were investigated using the microcapsule agglutination test (MCAT) for leptospirosis. The overall sensitivity (90.2%), specificity (96.3%), positive predictive value (94.9%), negative predictive value (92.9%), and accuracy of the MCAT (93.7%) were encouraging. MCAT is simple, can be performed by unskilled personnel with minimum laboratory facilities, and produces results in 3 h. MCAT would be a reliable serodiagnostic test for rapidly screening individuals for leptospirosis, in various geographical areas of Thailand.  相似文献   
56.
This paper introduces a new single-phase high power factor rectifier, which features regulation by conventional PWM, soft commutation and instantaneous average line current control. Furthermore, thanks to the use of a single converter, instead of the conventional configuration composed of a four-diode front-end rectifier followed by a boost converter, a significant reduction in the conduction losses is achieved. A prototype rated at 1.6 kW, operating at 70 kHz, with an input AC voltage of 220 Vrms and an output voltage of 400 VDC has been implemented in the laboratory. An efficiency of 97.8 % at 1.6 kW has been measured. Analysis, design, and the control circuitry are also presented in the paper  相似文献   
57.
We evaluated the effect of the image acquisition parameters on the accuracy of the principal axes and surface-fitting techniques for three-dimensional image registration. Using two types of phantom objects, MR brain image and a mathematically defined ellipsoid, we simulated pairs of scans with known acquisition parameters, including longitudinal coverage, magnitude of mis-registration, number of sections and section thickness. Both methods are sensitive to the systematic deformation of contours. The principal axes method is also sensitive to incomplete scan coverage and to the x-axis and y-axis misangulation. Both methods are insensitive to the number of sections, section thickness and the number of points per section. Surface fitting performed well without user supervision. There is no need for routine inclusion of the scaling factors as search parameters. The results confirm the feasibility of three-dimensional multimodality registration of brain scans with accuracy 1-2 mm, with surface fitting being the method of choice.  相似文献   
58.
Pantoprazole is a specific inhibitor of the H+/K(+)-ATPase of the gastric parietal cell. The dose-dependency of a range of pantoprazole pharmacokinetic characteristics was studied. Twelve healthy male subjects were given 10, 20, 40 and 80 mg pantoprazole intravenously according to a randomized, single blind, 4-period change-over scheme. The area under the concentration vs time curve (AUC) and the maximum serum concentration (Cmax) showed a linear increase in line with the dose. Apparent volume of distribution (Vd area), clearance (Cl) and terminal half-life (t1/2) were independent of the dose. The dose-independent elimination of pantoprazole was attributed to the lack of interaction of the drug with cytochrome P450. In clinical practice, a good predictable response, as well as a low potential for interaction with other drugs might be expected.  相似文献   
59.
60.
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