全文获取类型
收费全文 | 2591篇 |
免费 | 5篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 81篇 |
金属工艺 | 3篇 |
机械仪表 | 12篇 |
建筑科学 | 36篇 |
能源动力 | 5篇 |
轻工业 | 48篇 |
水利工程 | 11篇 |
石油天然气 | 1篇 |
无线电 | 78篇 |
一般工业技术 | 145篇 |
冶金工业 | 2104篇 |
原子能技术 | 4篇 |
自动化技术 | 66篇 |
出版年
2021年 | 6篇 |
2019年 | 3篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 13篇 |
2013年 | 20篇 |
2012年 | 12篇 |
2011年 | 21篇 |
2010年 | 17篇 |
2009年 | 17篇 |
2008年 | 25篇 |
2007年 | 24篇 |
2006年 | 30篇 |
2005年 | 20篇 |
2004年 | 18篇 |
2003年 | 21篇 |
2002年 | 11篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 76篇 |
1998年 | 623篇 |
1997年 | 348篇 |
1996年 | 218篇 |
1995年 | 140篇 |
1994年 | 135篇 |
1993年 | 127篇 |
1992年 | 35篇 |
1991年 | 48篇 |
1990年 | 36篇 |
1989年 | 56篇 |
1988年 | 45篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 32篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 21篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 57篇 |
1976年 | 128篇 |
1975年 | 4篇 |
1973年 | 7篇 |
1965年 | 3篇 |
1963年 | 3篇 |
1961年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有2596条查询结果,搜索用时 15 毫秒
61.
62.
CR Dudley B Keavney IM Stratton RC Turner PJ Ratcliffe 《Canadian Metallurgical Quarterly》1995,48(6):1907-1911
We performed a case-control study to determine whether molecular variants of genes of the renin-angiotensin system were associated with the presence of albuminuria in non-insulin dependent diabetes mellitus (NIDDM). A total of 180 diabetic patients with persistent microalbuminuria [median urinary albumin (interquartile range) of 74 (54 to 126 mg/liter)] were matched with two control groups of diabetic patients without microalbuminuria [median urinary albumin 7 (5 to 10) mg/liter] for variables known to be associated with raised urinary albumin concentration including hemoglobin A1c and triglyceride. One control group was also matched for blood pressure and the other group was not, to allow assessment of interactions with hypertension. Association with the I/D polymorphism of the ACE gene and M235T variant of the angiotensinogen gene (AGT) with microalbuminuria and retinopathy was examined. There were no significant differences in genotype frequency between cases and controls for ACE or AGT irrespective of blood pressure matching. However, among subjects with microalbuminuria, those with the ACE DD genotype had a significantly greater urinary albumin excretion than individuals with a non-DD genotype [median 88 (68 to 170) mg/liter vs. 67 (53 to 113) mg/liter, P < 0.001]. More subjects with the DD than non-DD genotype had persistent albuminuria > 100 mg/liter, twice the upper normal range (60% vs. 38%, P = 0.006). When increased albumin excretion occurs, the presence of the ACE DD genotype appears to be associated with higher urinary albumin levels. No association with retinopathy was observed. 相似文献
63.
64.
Concurrent infection is a risk factor for abdominal wound dehiscence. We reviewed our experience with fascial dehiscence to determine the incidence and to identify prognostic factors for associated intra-abdominal infection. Over a 7-year period, 107 patients with abdominal wound dehiscence were identified. Seventeen were managed nonoperatively, and 90 underwent exploratory laparotomy, 43 of whom had no intra-abdominal pathology and 47 of whom had intra-abdominal infections. Demographic factors, comorbid diseases, and potential indicators of systemic infection did not distinguish patients with intra-abdominal infection from those without. Patients with an intra-abdominal infection were more likely to have undergone an emergency operation (74% vs 48%; P < 0.02), an operation on the colon (55% vs 25%; P < 0.005), or an operation with a higher wound classification (P < 0.02). Mortality was higher in patients with intra-abdominal infection than in those without (44% vs 20%; P < 0.02). Wound dehiscence after emergent operations, and operations with a higher wound classification, especially those involving the colon, should raise concern for intra-abdominal infection. Thorough abdominal exploration should be performed at the time of dehiscence repair. Before nonoperative management is chosen, intra-abdominal infection should be excluded. 相似文献
65.
A. J. Armstrong B. W. James G. H. Wostenholm B. Yates J. Burgoine J. Eastham 《Journal of Materials Science》1986,21(12):4289-4295
The account describes investigations into the variations of specific volume and viscosity of a typical high-performance epoxy resin during various time-temperature cycles. The work was undertaken primarily to provide additional background information relating to the nature and causes of fibre kinking which has been observed in laminates comprising epoxy-carbon composite. The investigation has quantified certain characteristics of the resin which are presumed to be major contributory factors in the occurrence of fibre kinking. It is concluded that a simple solution to the general problem cannot be identified, although some possibilities are discussed for individual cases. 相似文献
66.
Andrew J. Morris Rebecca J. Nicholls Chris J. Pickard Jonathan R. Yates 《Computer Physics Communications》2014
We present OptaDOS, a program for calculating core-electron and low-loss electron energy loss spectra (EELS) and optical spectra along with total-, projected- and joint-density of electronic states (DOS) from single-particle eigenenergies and dipole transition coefficients. Energy-loss spectroscopy is an important tool for probing bonding within a material. Interpreting these spectra can be aided by first principles calculations. The spectra are generated from the eigenenergies through integration over the Brillouin zone. An important feature of this code is that this integration is performed using a choice of adaptive or linear extrapolation broadening methods which we show produces higher accuracy spectra than standard fixed-width Gaussian broadening. OptaDOS may be straightforwardly interfaced to any electronic structure code. OptaDOS is freely available under the GNU General Public licence from http://www.optados.org. 相似文献
67.
Kinetic expressions used to describe the reactions of deactivating catalyst particles are applied here to the sulphation of calcined limestone in a fluidised bed coal combustor where reactivity diminishes as pores fill with sulphate. Following closely the recent work of Fieldes and Davidson it is shown how experiments with batchwise addition of limestone to the combustor may be used to derive the two reaction rate constants of the system, ks, and kd, and how these may be incorporated into a two-phase model of a fluidised bed reactor to obtain predictions of desulphurisation efficiency under conditions of continuous operation. The resulting equation for SO2 retention, η, may be simplified to:η = 1 ? [] where K is a function of limestone type and operating conditions and β is the calcium-to-sulphur mole ratio. The predictions of this equation are shown to be in agreement with experimental results. 相似文献
68.
Measurements have been made of the absorption properties of a silicone fluid in a silicone elastomer, Aircast 3700, at temperatures between 0 and 150 °C. It was found that the diffusivity could be described by Arrhenius' law. The saturation fluid content was 20% at 0 °C, decreasing to 17% at 120 °C. The swelling was large, up to 26% at saturation, and approximately equalled the volume of fluid absorbed. A reverse thermal effect was observed and an attempt has been made to explain it. 相似文献
69.
CR McCarthy 《Canadian Metallurgical Quarterly》1994,69(9):695-698
The author provides a historical context for the difficult ethical and clinical issues associated with the inclusion of women and members of minority groups in clinical research. He cites as a point of departure the Nuremberg Code of the late 1940s, which declared the fundamental dignity of human beings involved as research subjects, a principle that was quickly endorsed worldwide. From the period following World War II through the 1970s, the prevailing attitude--not always practiced--toward research subjects in the United States was that they should be protected from exploitation. That attitude was reflected in the first broad federal policy on research subjects, created in 1966. During those years, research was widely regarded by the public as dangerous and of little value to individual participants; it is remarkable that so many men and women consented to participate in clinical studies at that time. Furthermore, during the 1970s, for reasons explained by the author, various events--the abortion debate, disclosures from the infamous Tuskegee syphilis study, Nixon's "war on cancer," new federal regulations in 1974 and 1975 (the latter providing additional protection for pregnant women in research), the broad interpretation of the FDA's 1977 policy excluding pregnant or potentially pregnant women from clinical trials, and the tendency of blacks and persons from other minority groups to shun participation in research--tended to deter participation of women and members of minority groups in clinical research.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
70.
We have studied the efficacy of two extradural infusions (10 ml h-1) in 50 patients in active labour. Patients in the diamorphine group (n = 25) received 0.0625% plain bupivacaine 6.25 mg h-1 mixed with 0.005% diamorphine 0.5 mg h-1 and those in the control group (n = 25) received 0.125% plain bupivacaine 12.5 mg h-1. Both groups received intermittent "top-ups" of 0.25% bupivacaine 10 ml when indicated. Although median pain scores during the infusion were similar in both groups, patients in the diamorphine group indicated greater satisfaction with the infusion (88% very satisfied, compared with 52% in the control group (P < 0.02)). There were no differences in the incidence of hypotension, instrumental vaginal delivery, number of "top-ups", duration of the second stage or extent of motor block. However, patients in the diamorphine group had a high incidence of pruritus (44%, compared with 0% in the control group (P < 0.01)). 相似文献