全文获取类型
收费全文 | 498573篇 |
免费 | 6307篇 |
国内免费 | 1629篇 |
专业分类
电工技术 | 8575篇 |
综合类 | 350篇 |
化学工业 | 76465篇 |
金属工艺 | 18626篇 |
机械仪表 | 14658篇 |
建筑科学 | 12629篇 |
矿业工程 | 2318篇 |
能源动力 | 12880篇 |
轻工业 | 48551篇 |
水利工程 | 4951篇 |
石油天然气 | 8812篇 |
武器工业 | 22篇 |
无线电 | 59288篇 |
一般工业技术 | 95153篇 |
冶金工业 | 91119篇 |
原子能技术 | 10128篇 |
自动化技术 | 41984篇 |
出版年
2021年 | 3661篇 |
2019年 | 3376篇 |
2018年 | 5756篇 |
2017年 | 5788篇 |
2016年 | 6364篇 |
2015年 | 4318篇 |
2014年 | 7317篇 |
2013年 | 22203篇 |
2012年 | 12386篇 |
2011年 | 17352篇 |
2010年 | 13849篇 |
2009年 | 15649篇 |
2008年 | 16311篇 |
2007年 | 16234篇 |
2006年 | 14684篇 |
2005年 | 13569篇 |
2004年 | 12842篇 |
2003年 | 12574篇 |
2002年 | 12220篇 |
2001年 | 12356篇 |
2000年 | 11431篇 |
1999年 | 11957篇 |
1998年 | 28435篇 |
1997年 | 20380篇 |
1996年 | 15804篇 |
1995年 | 12016篇 |
1994年 | 10619篇 |
1993年 | 10456篇 |
1992年 | 7842篇 |
1991年 | 7546篇 |
1990年 | 7234篇 |
1989年 | 7124篇 |
1988年 | 6963篇 |
1987年 | 5782篇 |
1986年 | 5686篇 |
1985年 | 6843篇 |
1984年 | 6350篇 |
1983年 | 5772篇 |
1982年 | 5410篇 |
1981年 | 5572篇 |
1980年 | 5280篇 |
1979年 | 5098篇 |
1978年 | 5019篇 |
1977年 | 5779篇 |
1976年 | 7381篇 |
1975年 | 4488篇 |
1974年 | 4279篇 |
1973年 | 4322篇 |
1972年 | 3625篇 |
1971年 | 3352篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
J Gálvez R García-Domenech C de Gregorio Alapont JV de Julián-Ortiz L Popa 《Canadian Metallurgical Quarterly》1996,14(5):272-276
BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives. 相似文献
993.
We determined the nucleotide sequence of the SH gene its flanking regions over a range of 380 nucleotides for three distinct mumps virus (MUV) isolates. Two isolates from the 1992 mumps epidemic in Western Switzerland and one MUV isolated in 1995 in the same geographic area have been analyzed and compared to 16 recently published SH nucleotide sequences and their presumed amino acid sequences. The nucleotide sequences from the 1992 MUV isolates were identical and closely related to two MUV strains from Eastern Switzerland and strains from the U.K. The MUV isolated in 1995 is clearly different from all other strains. 相似文献
994.
M Suda K Tanaka K Natsui T Usui I Tanaka M Fukushima C Shigeno J Konishi S Narumiya A Ichikawa N Nakao 《Canadian Metallurgical Quarterly》1996,137(5):1698-1705
PGE2 is one of the key molecules in the osteoblast. It is the major prostanoid in the bone, and its production is under the control of both systemic and local factors. PGE2 has been reported to have multiple actions in the osteoblast, such as growth promotion and cell differentiation. To better understand the action of PGE2 in the osteoblast, we determined the PGE receptor subtypes in MC3T3-E1, an osteoblastic cell line derived from the normal mouse calvaria. Northern blot analysis revealed that EP1 and EP4 subtypes are expressed in MC3T3-E1. In contrast, EP3 subtype was not detected by either Northern blot analysis or RT-PCR. The contribution of each subtype was evaluated by studying the effects of subtype-specific analogs on osteoblastic function at confluency and 5 days after confluency. An EP1 agonist, 17-phenyl-omega-trinor PGE2, increased DNA synthesis and decreased alkaline phosphatase activity. 11-Deoxy-PGE1, and EP2 and EP4 agonist, decreased DNA synthesis and increased alkaline phosphatase activity at both stages. Butaprost, an EP2-selective agonist, showed effects similar to those of 11-deoxy-PGE1 only at confluency. Another and more differentiated osteoblastic marker, osteocalcin production, was detectable and was stimulated by 11-deoxy-PGE1 only 5 days after confluency. The exposure of these cells to EP1 agonist changed the cell shape to a more fibroblastic appearance. These results indicate that EP1, EP4, and probably EP2 are present in MC3T3-E1 cells; EP1 promotes cell growth, and EP2 and EP4 mediate differentiation of the osteoblast. Furthermore, the decreased response to EP2-specific agonist 5 days after confluency suggests that the expression of PGE receptor subtype is dependent on the stage of osteoblastic differentiation. This is the first report to determine PGE receptor subtypes in the bone. 相似文献
995.
Amador F.G. Berman D. Borning A. DeRose T. Finkelstein A. Neville D. Notkin D. Salesin D. Salisbury M. Sherman J. Sun Y. Weld D.S. Winkenbach G. 《Knowledge and Data Engineering, IEEE Transactions on》1993,5(4):611-618
The electronic encyclopedia exploratorium (E3) is a vision of a future computer system-an electronic book describing how thing work. Typical articles in E3 will describe such mechanisms as compression refrigerators, engines, telescopes, and mechanical linkages. Each article will provide simulations, three-dimensional animated graphics that the user can manipulate, laboratory areas that allow a user to modify the device or experiment with related artifacts, and a facility for asking questions and receiving customized, computer-generated English-language explanations. Some of the foundational technology is discussed, focusing on topics in artificial intelligence, graphics, and user interfaces. The initial prototype system and the technical lessons learned from it, as well as the second prototype currently under construction, are described 相似文献
996.
997.
J Lorenz K Wilhelm M Kessler C Peschel U Schwulera R Lissner WG Struff E Huland C Huber WE Aulitzky 《Canadian Metallurgical Quarterly》1996,2(7):1115-1122
Safety, local and systemic immunomodulation, and tumor response to treatment with aerosolized natural interleukin 2 (nIL-2) applied five times a day were studied in a Phase I trial in 16 patients with pulmonary malignancies refractory to conventional therapy. The toxicity of inhaled nIL-2 was different from that observed after systemic administration. Reversible airway irritation causing a nonproductive cough represented the dose-limiting toxicity. Mild to moderate reduction of the vital capacity and forced expiratory volume (FEV1) with minor effects on relative FEV1, peak expiratory flow, airway resistance, and PaO2 was experienced by individual patients. In 14 patients suffering from pulmonary metastases due to renal cell cancer, one durable complete response, one partial response, and one mixed response were observed. Inhalation of nIL-2 aerosol resulted in a dose-dependent expansion of pulmonary immunocompetent cells in bronchoalveolar lavage fluid. Posttreatment bronchoalveolar lavage showed an activated lymphocyte phenotype with increased HLA-DR expression. The only systemic biological effect detectable in peripheral blood was a marked increase of soluble interleukin 2 receptor serum levels. We conclude that treatment with aerosolized nIL-2 is an effective means for site-specific immunomodulation and deserves further investigation for the treatment of malignant and inflammatory lung disease. 相似文献
998.
The mechanism of “475°C embrittlement” of a duplex stainless steel was investigated using finite element modelling of the stress distribution at brittle fracture initiation. Brittle fracture initiated at a critical shear stress, which increased with ferrite hardness. The fracture stress was affected by the duplex microstructure. Fracture was nucleated by deformation twins, which were identified using electron back-scatter diffraction. The ductile-to-brittle fracture transition was sensitive to age-hardening and could be described simply by the effect of age-hardening and test temperature on the yield stress. 相似文献
999.
Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 6, pp. 88–98, November–December, 1996. 相似文献
1000.
J. S. Kim D. G. Seiler R. A. Lancaster M. B. Reine 《Journal of Electronic Materials》1996,25(8):1215-1220
Variable-magnetic-field Hall measurements (0 to 1.5 T) are performed on very-narrow-gap bulk-grown Hg1−xCdxTe single crystals (0.165 ≤ x ≤ 0.2) at various temperatures (10 to 300K). The electron densities and mobilities are obtained
within the one-carrier (electrons) approximation of the reduced-con-ductivity-tensor scheme. The present data together with
the selected data set reported by other workers exhibit a pronounced peak when the electron mobility is plotted against the
alloy composition x-value which has been predicted to be due to the effective-mass minimum at the bandgap-crossing (Eg ≈ 0). The observed position (x ≈ 0.165), height (≈4 x 102 m2Vs), and width (≈0.01 in x) of the mobility-peak can be explained by a simple simulation involving only ionized-impurity scattering.
A lower bound of the effective mass is introduced as a fitting parameter to be consistent with the finiteness of the observed
electron mobility and is found to be of the order of 10−4 of the mass of a free electron. 相似文献