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   3334篇
  免费   11篇
  国内免费   2篇
电工技术   20篇
综合类   2篇
化学工业   104篇
金属工艺   34篇
机械仪表   64篇
建筑科学   24篇
矿业工程   9篇
能源动力   3篇
轻工业   56篇
水利工程   35篇
石油天然气   42篇
武器工业   1篇
无线电   102篇
一般工业技术   214篇
冶金工业   2457篇
原子能技术   157篇
自动化技术   23篇
  2021年   11篇
  2020年   14篇
  2019年   16篇
  2018年   36篇
  2017年   50篇
  2016年   33篇
  2015年   11篇
  2014年   25篇
  2013年   38篇
  2012年   25篇
  2011年   45篇
  2010年   33篇
  2009年   27篇
  2008年   36篇
  2007年   25篇
  2006年   28篇
  2005年   18篇
  2004年   13篇
  2003年   20篇
  2002年   17篇
  2001年   27篇
  2000年   15篇
  1999年   83篇
  1998年   743篇
  1997年   407篇
  1996年   286篇
  1995年   177篇
  1994年   119篇
  1993年   166篇
  1992年   26篇
  1991年   35篇
  1990年   41篇
  1989年   44篇
  1988年   46篇
  1987年   25篇
  1986年   28篇
  1985年   22篇
  1984年   11篇
  1982年   19篇
  1981年   23篇
  1980年   35篇
  1979年   14篇
  1978年   16篇
  1977年   86篇
  1976年   198篇
  1973年   11篇
  1972年   13篇
  1970年   11篇
  1969年   11篇
  1967年   10篇
排序方式: 共有3347条查询结果,搜索用时 31 毫秒
71.
The etiology of liver disease remains unknown in about 4 to 23% of dialysis patients and 10 to 16% of renal transplant recipients. A search for other causative agents of liver disease led to the discovery of the GB group of viruses. We studied the association between the presence of GB virus C (GBV-C) infection, known risk factors for parenterally-transmitted infections and history or laboratory evidence of liver disease among end-stage renal disease (ESRD) patients referred for renal transplantation to the New England Organ Bank, MA. Stored sera from patients on the renal transplantation waiting list between November 1986 and June 1990 were tested for antibody to hepatitis C virus (HCV). Sera were available in 1544 of 3243 (48%) patients, and anti-HCV was detected by ELISA3 in 287 (19%). All 287 anti-HCV positive patients formed the anti-HCV positive cohort and 286 randomly selected anti-HCV negative patients formed the anti-HCV negative cohort (573 patients overall). Additional sera were available for GBV-C RNA testing in 465 of 573 (81%) patients, and GBV-C RNA was detected by RT-PCR in 146. The overall extrapolated prevalence of serum GBV-C RNA was 29%. The prevalence of serum GBV-C RNa among anti-HCV positive patients (35%) was not significantly different from that among anti-HCV negative patients (29%; P = 0.22). In a univariate analysis, compared to patients without GBV-C RNA, patients with serum GBV-C RNA were younger [odds ratio (OR) 0.98 per year of age, P = 0.01], had a lower proportion of males (OR 0.64, P = 0.03), lower proportion of patients with diabetes mellitus (OR 0.44, P = 0.01), higher proportion of patients with a previous transplantation (OR 1.53, P = 0.04), longer duration of dialysis at the time of enrollment (OR 1.004 per month on dialysis, P = 0.03), and a higher proportion of patients with history of transfusions (OR 4.58, P = 0.01). Serum GBV-C RNA was not associated with a significantly increased OR for history of liver disease or non-A, non-B hepatitis, or elevated serum alanine aminotransferase levels. In a step-wise multivariate regression analysis, a younger age (OR 0.98 per year of age, P = 0.03), and history of blood transfusions (OR 3.89, P = 0.03) were associated with an increased OR for serum GBV-C RNA, while diabetes mellitus was associated with a decreased OR for GBV-C RNA (OR 0.47, P = 0.01). Anti-HCV was not a predictor of serum GBV-C RNA (OR 1.07, P = 0.77). The results of this study support the fact that GBV-C is a parenterally transmitted virus and shed light on the modes of transmission of GBV-C among ESRD patients. However, the association with liver disease remains to be established.  相似文献   
72.
73.
PURPOSE: To evaluate in a prospective study the efficacy of autologous bone marrow transplantation (BMT) in adult patients with acute myelogenous leukemia (AML) in first remission, using a single course of high-dose Cytarabine (HD Ara-C) consolidation therapy as in vivo purging. PATIENTS AND METHODS: Sixty consecutive adult patients with AML in first complete remission (CR) were treated with HD Ara-C consolidation therapy as a method of in vivo purging before marrow collection. High-dose therapy consisted of fractionated total-body irradiation (FTBI) 12 Gy, intravenous etoposide 60 mg/kg, and cyclophosphamide 75 mg/kg, followed by reinfusion of cryopreserved marrow. RESULTS: Sixty patients underwent consolidation treatment with HD Ara-C with the intent to treat with autologous BMT. Sixteen patients were unable to proceed to autologous BMT (10 patients relapsed, one died of sepsis, one developed cerebellar toxicity, two had inadequate blood counts, and two refused). Forty-four patients underwent autologous BMT and have a median follow-up time of 37 months (range, 14.7 to 68.7) for patients who are alive with no relapse. The cumulative probability of disease-free survival (DFS) at 24 months in the intent-to-treat group is 49% (95% confidence interval [CI], 37% to 62%) and in those who actually underwent autologous BMT is 61% (95% CI, 46% to 74%). The probability of relapse was 44% (95% CI, 31% to 58%) and 33% (95% CI, 20% to 49%) for the intent-to-treat and autologous BMT patients, respectively. CONCLUSION: This approach offers a relatively high DFS rate to adult patients with AML in first CR. The results of this study are similar to those achieved with allogeneic BMT.  相似文献   
74.
The present study investigates 1085 previously untreated patients with squamous cell carcinoma of the head and neck for factors that influence recurrence following treatment with definitive radiotherapy. In the second part of this study, those diagnosed with recurrence were studied with regard to treatment and were further analysed with regard to identification of prognostic factors which may affect outcome in the patient who actually develops a recurrence.  相似文献   
75.
A novel chitinase gene of tobacco was isolated and characterized by DNA sequence analysis of a genomic clone and a cDNA clone. Comparative sequence analysis of both clones showed an identity of 94%. The proteins encoded by these sequences do not correspond to any of the previously characterized plant chitinases of classes I-IV and are designated as class V chitinases. Comparison of the chitinase class V peptide sequence with sequences in the Swiss Protein databank revealed significant sequence similarity with bacterial exo-chitinases from Bacillus circulans, Serratia marcescens and Streptomyces plicatus. It was demonstrated that class V chitinase gene expression is induced after treatment of tobacco with different forms of stress, like TMV-infection, ethylene treatment, wounding or ultraviolet irradiation. Two related chitinase class V proteins of 41 and 43 kDa were purified from Samsun NN tobacco leaves inoculated with tobacco mosaic virus. The proteins were purified by Chelating Superose chromatography and gel filtration. In vitro assays demonstrated that class V chitinases have endo-chitinase activity and exhibit antifungal activity toward Trichoderma viride and Alternaria radicina. In addition, it was shown that class V chitinase acts synergistically with tobacco class I beta-1,3-glucanase against Fusarium solani germlings.  相似文献   
76.
1.  The side curtains as necessary cutoff elements of the al-Qadisiyah hydro development were made in an optimal design variant, on time, and with a high quality. A considerable technical and economic effect was obtained by eliminating excessive volumes of works specified by the original design as a result of a combined analysis of the data of engineering surveys, investigations of experimental grouting works, and optimization of the grouting technology.
2.  The index of unit cement absorption in the control holes used as the criterion of sufficiency of grouting on the side curtains should be used everywhere where the purpose of grouting works is to detect and eliminate large cavities and fissures.
3.  Grouting works on elimination of karst cavities and large fissures, being in essence infill grouting, require the development of an industrial technology of the works with the use of considerable volumes of grouts (concretes) and use of a large number of machines and mechanisms (concrete plants, mixers, concrete pumps, etc.).
Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 1, pp. 45–50, January, 1989.  相似文献   
77.
1.  Polymer-cement shotcrete (gunite) has a number of advantages in comparison with ordinary shotcrete — increased elasticity (low modulus of deformation), high impermeability and adhesiveness to rocks and concrete, resistance to corrosive effects, nontoxicity of the polymer used, and simplicity of the technology of adding latex to the coating material.
2.  The addition of polymer makes it possible to reduce the thickness of the coating by at least half while preserving the strength and operating characteristics of the support, which provides a high cost effectiveness of using polymer-cement shotcrete.
3.  It is expedient to recommend the wide use of highly effective polymer-cement compositions on a base of synthetic latex SKS-65GP in hydrotechnical construction.
Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 7, pp. 18–22, July, 1988.  相似文献   
78.
1.  It is necessary to correlate the value of the noneroding velocity with the time of flood passage. If canals are planned in regions where comparatively brief summer floods are dominant, the value of the noneroding velocity should be taken equal to 3 m/sec since by the start of the flood the grass cover will have time to develop and reach maximum strength. If the canals are to be constructed in regions where spring floods are dominant, for example, in the northwestern regions of the country, then the noneroding velocity should be taken equal to 1.5 m/sec, since by the start of the flood the grass carpet does not have time to develop and become stronger.
2.  In the absence of a constant runoff in the canal, for example, drainage canals, it is necessary to revet the bottom and side slopes with grass carpets.
3.  In the presence of a constant moistening is made from traditional materials, in the zone of alternate moistening and above it, it is necessary to revet the slopes within reinforced grass carpet.
4.  In a hydraulic calculation of canals with revetment of the bottom and side slopes with grass carpet, it is necessary to determine the roughness coefficient from the graph of n=f(VR, i). In a hydraulic calculation of wide overgrown channels and in calculation of the movement of the flow over floodplain stretches of rivers free from shrubs and trees, it is necessary to determine the roughness coefficient from the graph of n=f(Vh, i).
5.  Calculation of canals with nonuniform roughness (rigid revetment and revetment by grass carpets) must be carried out on the basis of relations of uniform flow by means of a generalized roughness coefficient.
A method of hydraulic calculation of canals with revetment by grass carpets with presentation of an algorithm and calculation examples was developed from the results of the studies.  相似文献   
79.
An exact differential equation for the equilibrium of an elastic fibre loaded on the free end with a concentrated force and over the entire length of the elastic line of the distributed power load caused by the weight of the fibre was obtained in conditions of large movements. A method was developed for determining the flexural rigidity of the fibre which consists of bending the fibres and numerically solving the equation from the geometric nonlinear theory of bending of elastic fibres. __________ Translated from Khimicheskie Volokna, No. 4, pp. 19–21, July–August, 2007.  相似文献   
80.
A strategy of industrial-scale manufacture for a wide range of carbon materials based on carbon nanofibers is proposed. It was shown that porous materials with a high sorption capacity can be obtained with the use of carbon nanofibers by means of conventional manufacturing operations. The results of studying of consolidation of carbon nanofibers with pyrolytic carbon are reported. It was found that the nature of carbon material has a substantial effect on the rate of deposition of pyrolytic carbon. The most appropriate temperature range in which carbon nanofibers should be consolidated for the preparation of materials with a high catalytic activity was determined.  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