全文获取类型
收费全文 | 4853篇 |
免费 | 110篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 41篇 |
综合类 | 9篇 |
化学工业 | 402篇 |
金属工艺 | 67篇 |
机械仪表 | 59篇 |
建筑科学 | 118篇 |
矿业工程 | 12篇 |
能源动力 | 108篇 |
轻工业 | 348篇 |
水利工程 | 41篇 |
石油天然气 | 19篇 |
无线电 | 253篇 |
一般工业技术 | 368篇 |
冶金工业 | 2659篇 |
原子能技术 | 26篇 |
自动化技术 | 449篇 |
出版年
2022年 | 30篇 |
2021年 | 36篇 |
2020年 | 32篇 |
2019年 | 21篇 |
2018年 | 51篇 |
2017年 | 34篇 |
2016年 | 46篇 |
2015年 | 50篇 |
2014年 | 87篇 |
2013年 | 143篇 |
2012年 | 92篇 |
2011年 | 117篇 |
2010年 | 98篇 |
2009年 | 85篇 |
2008年 | 101篇 |
2007年 | 113篇 |
2006年 | 103篇 |
2005年 | 79篇 |
2004年 | 71篇 |
2003年 | 86篇 |
2002年 | 76篇 |
2001年 | 71篇 |
2000年 | 62篇 |
1999年 | 118篇 |
1998年 | 874篇 |
1997年 | 535篇 |
1996年 | 326篇 |
1995年 | 174篇 |
1994年 | 171篇 |
1993年 | 180篇 |
1992年 | 53篇 |
1991年 | 59篇 |
1990年 | 47篇 |
1989年 | 61篇 |
1988年 | 59篇 |
1987年 | 50篇 |
1986年 | 34篇 |
1985年 | 39篇 |
1984年 | 21篇 |
1983年 | 24篇 |
1982年 | 20篇 |
1981年 | 25篇 |
1980年 | 37篇 |
1978年 | 17篇 |
1977年 | 72篇 |
1976年 | 146篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 19篇 |
1972年 | 13篇 |
排序方式: 共有4979条查询结果,搜索用时 15 毫秒
1.
D Galasko T Saitoh Y Xia LJ Thal R Katzman LR Hill L Hansen 《Canadian Metallurgical Quarterly》1994,44(10):1950-1951
We determined apolipoprotein E (ApoE) genotypes in 122 autopsied demented patients. The frequency of the ApoE epsilon 4 allele was 39.6% in Alzheimer's disease (AD), 29.0% in the Lewy body variant of AD (LBV), and 6.25% in diffuse Lewy body disease. For AD and LBV patients, the epsilon 4 frequency was significantly higher than that reported in nondemented controls (10 to 15%). Therefore, LBV and AD share ApoE epsilon 4 as a genetic risk factor, providing further evidence that these conditions overlap. 相似文献
2.
3.
BACKGROUND: The enterococci have become important nosocomial pathogens. They can cause multiple site infections and enterococcal bacteremia becomes more frequently associated with a high mortality rate. Previous studies of enterococcal bacteremia showed a variety of results. To establish the significance and importance of enterococci as nosocomial pathogens in this hospital, to characterize their clinical pictures and to search for the risk factors for mortality, this retrospective study was performed. METHODS: There were 208 cases of enterococcal bacteremia which occurred from 1988 to 1992. Twenty-seven cases had no medical charts, dismissing possibility of evaluation. Finally, 181 cases of enterococcal bacteremia were analysed. RESULTS: One hundred and eighteen episodes were nosocomial infections. Polymicrobial bacteremia occurred in 68.5% of the patients and the most common co-isolate was Pseudomonas aeruginosa. Those patients (78.5%) with underlying diseases and malignancies were the most common underlying problems. The portal of entry could be found in 69.6 percent of patients, with the gastrointestinal tract the most common sources. Antimicrobial susceptibility testing showed high gentamicin resistance rate (89.5%), and ampicillin still had about 80 percent sensitivity rate. The group who received specific antibiotic therapy for enterococcus showed lower mortality (36.4% versus 47.6%). Only one case had infective endocarditis. Forty-nine patients suffered from septic shock, the cause of 30 deaths. Totally 75 patients died during hospitalization. Besides sepsis, another major cause of death was their underlying diseases itself. CONCLUSIONS: Enterococci have no doubt become important nosocomial pathogens and enterococcal bacteremia were associated with high mortality, especially in elderly patients with underlying diseases such as malignancy or diabetes. When clinically dealing with sepsis from the gastrointestinal or biliary tract, especially when previous cephalosporins therapy showed no response, the possibility of enterococcal bacteremia should always be considered. 相似文献
4.
5.
Steven Y. Susswein Thomas C. Henderson Joseph L. Zachary Chuck Hansen Paul Hinker Gary C. Marsden 《International journal of parallel programming》1991,20(6):453-473
Filtering algorithms are well accepted as a means of speeding up the solution of the consistent labeling problem (CLP). Despite the fact that path consistency does a better job of filtering than arc consistency, AC is still the preferred technique because it has a much lower time complexity. We are implementing parallel path consistency algorithms on multiprocessors and comparing their performance to the best sequential and parallel arc consistency algorithms.(1,2) (See also work by Kerethoet al.
(3) and Kasif(4)) Preliminary work has shown linear performance increases for parallelized path consistency and also shown that in many cases performance is significantly better than the theoretical worst case. These two results lead us to believe that parallel path consistency may be a superior filtering technique. Finally, we have implemented path consistency as an outer product computation and have obtained good results (e.g., linear speedup on a 64K-node Connection Machine 2). 相似文献
6.
重馏分油加氢脱氮反应动力学模型的研究 总被引:10,自引:1,他引:9
简要地介绍了一些典型的模型氮化物的HDN反应规律。根据胜利VGO在3722B催化剂上的大量HDN实验数据,提出了如下的HDN基本反应动力学方程:dCNdt=-k1+K*CNCNPH2为了扩大上式的应用范围,详细分析了各种因素(如原料油种类和馏程及H2S等)对HDN的影响,并开发了相应的经验关联式,从而得到了一个较完整的馏分油HDN反应动力学模型。验证实验表明,该模型是成功的。 相似文献
7.
We describe in this report a sensitive and direct method for the analysis of tamoxifen (TAM) in microsamples of plasma. The drug and internal standard (quinine bisulfate, I.S.) were separated on a 10-microm particle, 10 cm X 8 mm CN cartridge in conjunction with a radial compression system. The mobile phase was a mixture of 0.1 M sodium acetate in 0.001 M tetrabutylammonium phosphate solution (pH 6) and methanol (30:70, v/v) at a flow-rate of 4 ml/min. After addition of I.S. and o-phosphoric acid in acetonitrile (0.6 M) to the plasma (30 microl), the mixture was placed in an ultraviolet shortwave transluminator for 2 min prior to injection into the chromatograph. The compounds were detected in the effluent fluorometrically at excitation and emission wavelengths of 258 and 378 nm, respectively. Under these conditions, no interference in the assay from any endogenous substance or other concurrently used drugs was observed and the retention times of I.S. and TAM were 4.4 and 10.15 min, respectively. The concentration of TAM in plasma was linearly (r>0.9983) related to the peak height ratio (TAM/I.S.) in the range 0.01-2.0 microg ml(-1) and C.V. at 0.075, 0.4 and 1.2 microg ml(-1) was < or = 4.96%. We are currently using this assay for monitoring TAM in plasma and investigating its pharmacokinetics in cancer patients receiving cytotoxic drugs in addition to TAM as a multi-drug resistance modifier. 相似文献
8.
CH Alleyne TH Fox JJ Olson GA Cotsonis I Crocker RA Bakay 《Canadian Metallurgical Quarterly》1997,5(1):20-30
The objective of this survey was to demonstrate whether a primary care track internal medicine residency program emphasizing community-based health care of the urban sick poor trains physicians who will continue to practice in general internal medicine or similar fields. Thirty-five primary care residents (100% of graduates) who trained from 1976 through 1993 in the Adult Primary Care Track of the Internal Medicine Residency Program at St. Vincent's Hospital, New York were used as participants. 相似文献
9.
The homogeneity of comminuted composites of 20 lb samples of apples, cabbage, and green beans containing field-incurred residues of p, p'-methoxychlor was studied to determine whether a 5 min comminution in a 40 qt vertical cutter mixer produces a homogeneous composite and whether the size of test portions used accurately represents the composite. Duplicate test portions of 100, 50, 25, 10, 5, and 2 g taken from each of 6 separate sections of the mixer were analyzed by standard pesticide residue methodology for p, p'-methoxychlor. Results of this study confirmed that comminution of fresh produce in a 40 qt vertical cutter mixer, according to instructions described in the U.S. Food and Drug Administration's Pesticide Analytical Manual, Volume I, Section 203B, produces a homogeneous composite. No significant differences were found in the data for the 3 crops taken from the 6 sections of the mixer. Test portion weights of 100, 50, and 25 g produced equivalent results for all 3 crops. Statistically significant differences were observed for cabbage at 2, 5, and 10 g and for green beans at 2 g. 相似文献
10.
A method was developed for administering intrathecal pharmacotherapy in a rat model of spinal cord injury. The effects of intrathecal administration of nimodipine on spinal cord blood flow (SCBF) and evoked potentials (EPs) were measured in the normal and injured spinal cord. It had previously been shown that systemic nimodipine caused severe hypotension after spinal cord injury. After baseline SCBF and EPs, 15 uninjured rats were blindly allocated to one of three groups: one placebo group (n = 5); and two groups with intrathecal nimodipine, 0.05 mg/kg (n = 5), or 0.2 mg/kg (n = 5). Ten other rats received a 35 g acute clip compression injury of the spinal cord for 1 minute and, were allocated to one of two groups: placebo (n = 5); and intrathecal nimodipine 0.05 mg/kg (n = 5) given 60 min after injury. In the uninjured groups, neither 0.05 nor 0.2 mg/kg of nimodipine increased SCBF during, or 30 min after, intrathecal infusion. However, the mean arterial blood pressure (MABP) decreased significantly to 69.73.1% after the infusion of 0.2 mg/kg nimodipine and did not recover by 98 min. In all three groups of uninjured rats, the amplitude of the cerebellar EP was decreased 30 min after infusion. After spinal cord injury, there were significant decreases in MABP, SCBF and EP amplitude in both placebo and treatment groups, but there was no therapeutic benefit from nimodipine. Thus, intrathecal infusion of nimodipine did not prevent the hypotension encountered with systemic administration and exerted no beneficial effect on SCBF or EPs after acute spinal cord injury. 相似文献