全文获取类型
收费全文 | 199440篇 |
免费 | 2571篇 |
国内免费 | 611篇 |
专业分类
电工技术 | 3468篇 |
综合类 | 149篇 |
化学工业 | 28979篇 |
金属工艺 | 8049篇 |
机械仪表 | 6068篇 |
建筑科学 | 4811篇 |
矿业工程 | 1303篇 |
能源动力 | 5127篇 |
轻工业 | 17119篇 |
水利工程 | 2297篇 |
石油天然气 | 4040篇 |
武器工业 | 8篇 |
无线电 | 23068篇 |
一般工业技术 | 40022篇 |
冶金工业 | 37227篇 |
原子能技术 | 5086篇 |
自动化技术 | 15801篇 |
出版年
2021年 | 1605篇 |
2019年 | 1569篇 |
2018年 | 2574篇 |
2017年 | 2646篇 |
2016年 | 2779篇 |
2015年 | 1794篇 |
2014年 | 3076篇 |
2013年 | 8947篇 |
2012年 | 5052篇 |
2011年 | 7029篇 |
2010年 | 5590篇 |
2009年 | 6352篇 |
2008年 | 6445篇 |
2007年 | 6513篇 |
2006年 | 5580篇 |
2005年 | 5228篇 |
2004年 | 5005篇 |
2003年 | 4887篇 |
2002年 | 4525篇 |
2001年 | 4656篇 |
2000年 | 4578篇 |
1999年 | 4726篇 |
1998年 | 11373篇 |
1997年 | 8120篇 |
1996年 | 6408篇 |
1995年 | 4673篇 |
1994年 | 4271篇 |
1993年 | 4073篇 |
1992年 | 3223篇 |
1991年 | 3076篇 |
1990年 | 2870篇 |
1989年 | 2951篇 |
1988年 | 2826篇 |
1987年 | 2398篇 |
1986年 | 2308篇 |
1985年 | 2715篇 |
1984年 | 2505篇 |
1983年 | 2345篇 |
1982年 | 2090篇 |
1981年 | 2203篇 |
1980年 | 2029篇 |
1979年 | 2124篇 |
1978年 | 2120篇 |
1977年 | 2366篇 |
1976年 | 3188篇 |
1975年 | 1833篇 |
1974年 | 1761篇 |
1973年 | 1772篇 |
1972年 | 1443篇 |
1971年 | 1339篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A justification is given for the conversion of pointer-reading manual gear measuring instruments to digital ones. The BV-5126
digital gear tooth micrometer and BV-5126 pitch gauge, both developed at NII-izmerieniya, are described. These instruments,
while retaining the advantages of mechanical manual instruments, are more convenient in use, and have smaller errors. Computer
software is also described which considerably widens the functional possibilities of the manual instruments.
Translated from Izmeritel'naya Tekhnika, No. 6, pp. 31–33, June, 1996. 相似文献
992.
An optoelectronic charge coupled device (OECCD) which is directly compatible with an incident optical signal is proposed. The nonlinear partial differential equation consisting of optical generation and recombination is solved in one dimension using the Crank-Nicolson finite-difference scheme. The charge transfer inefficiency is the main parameter considered for the calculation 相似文献
993.
A single randomized trial evaluated the use of intravenous cyclosporine treatment for severe attacks of ulcerative colitis. The perceived efficacy and safety of this intervention were measured through a survey of the membership of the Canadian Association of Gastroenterology (CAG). METHODS: All CAG members were mailed a survey with questions regarding their familiarity with the data supporting the use of cyclosporine, their perception of the efficacy and toxicity of the drug, and whether patients who fail conventional treatment should receive this therapy. The proportion of respondents who had used cyclosporine to treat severe ulcerative colitis was determined. RESULTS: One hundred and sixty-one responses were received (34% response rate). Sixty-four per cent of respondents were academic faculty members and 82% treated patients with severe colitis. Using multivariate analyses, positive associations were found between the respondents' age (P = 0.004) and subspecialty training in gastroenterology (P = 0.001), and whether respondents treat patients with severe ulcerative colitis. Twenty-six per cent of individuals had prescribed cyclosporine for this indication, of whom 88% were in academic practice (P = 0.007). Over 90% of respondents believe that further clinical trials are needed before cyclosporine becomes accepted as standard therapy. CONCLUSIONS: Although the use of cyclosporine is measurable among Canadian gastroenterologists, the majority believe that further clinical trials are necessary before the drug is accepted as a standard therapy. 相似文献
994.
The bit-error rate (BER) performance of new iterative decoding algorithms (e,g,, turbodecoding) is achieved at the expense of a computationally burdensome decoding procedure. We present a method called early detection that can be used to reduce the computational complexity of a variety of iterative decoders. Using a confidence criterion, some information symbols, state variables, and codeword symbols are detected early on during decoding. In this way, the computational complexity of further processing is reduced with a controllable increase in the BER. We present an easily implemented instance of this algorithm, called trellis splicing, that can be used with turbodecoding. For a simulated system of this type, we obtain a reduction in the computational complexity of up to a factor of four, relative to a turbodecoder that obtains the same increase in the BER by performing fewer iterations 相似文献
995.
996.
997.
Serologic evidence of previous Campylobacter jejuni infection in patients with the Guillain-Barré syndrome 总被引:1,自引:0,他引:1
B Mishu AA Ilyas CL Koski F Vriesendorp SD Cook FA Mithen MJ Blaser 《Canadian Metallurgical Quarterly》1993,118(12):947-953
OBJECTIVE: To determine if patients with the Guillain-Barré syndrome are likely to have had Campylobacter jejuni infection before onset of neurologic symptoms. DESIGN: A case-control study. SETTING: Several university medical centers. PATIENTS: Case patients met clinical criteria for the Guillain-Barré syndrome between 1983 and 1990 and had a serum sample collected and frozen within 3 weeks after onset of neurologic symptoms (n = 118). Disease controls were patients with other neurologic illnesses (n = 56); healthy controls were hospital employees or healthy family members of patients (n = 47). MEASUREMENTS: Serum IgA, IgG, and IgM antibodies to C. jejuni were determined by enzyme-linked immunosorbent assays. Assays were done in a blinded manner. RESULTS: Optical density ratios > or = 2 in two or more immunoglobulin classes were seen in 43 (36%) of patients with the Guillain-Barré syndrome and in 10 (10%) of controls (odds ratio, 5.3; 95% CI, 2.4 to 12.5; P < 0.001). Increasing the optical density ratio or the number of immunoglobulin classes necessary to yield a positive result increased the strength of the association. The number of patients with the Guillain-Barré syndrome who had positive serologic responses was greatest from September to November (P = 0.02). Male patients were three times more likely to have serologic evidence of C. jejuni infection (P = 0.009); the proportion of patients with the syndrome who had a positive serologic response increased with age. CONCLUSIONS: Patients with the Guillain-Barré syndrome are more likely than controls to have serologic evidence of C. jejuni infection in the weeks before onset of neurologic symptoms. Campylobacter jejuni may play a role in the initiation of the Guillain-Barré syndrome in many patients. 相似文献
998.
Binder M. Mammone R.J. Wade W.L. Jr. Rondeau E. Lavene B. 《Electrical Insulation Magazine, IEEE》1992,8(4):16-19
It is shown that the electrical breakdown voltages of polycarbonate film/metal foil capacitors can be increased. This can be achieved by briefly exposing the metal foil in these spirally wound film foil sections to a low-pressure, low-temperature gas plasma. Exposure of tin/lead foil to a 96% CF4/4% O2 gas plasma for four min, for example, produced >500% increase in breakdown voltage of sealed polycarbonate capacitors 相似文献
999.
OBJECTIVE: To determine the prognostic role of p53, Ki-67 and p21 for patients with muscle-invasive bladder cancer treated with curative intent by radiotherapy. PATIENTS AND METHODS: The study included 131 patients (24 women and 107 men, median age 72 years, range 40-86) with transitional cell carcinoma (T2-T4) treated with external definitive pelvic radiotherapy between 1985 and 1994. Paraffin-embedded pretreatment biopsies from the patients were examined for the presence of p53, p21 and Ki-67, detected by immunohistochemistry, and related to tumour stage, grade and patient survival. RESULTS: The expression of p53 protein correlated positively with the detection of Ki-67 (P < 0.05) but did not correlate with p21. None of the immunohistochemical variables (p53, p21 or Ki-67) correlated with T category and only Ki-67 correlated with histological grade. Patients with > 5% p21 expression tended to live longer than those with < 5% (P = 0.09). In a multivariate analysis, the T category (T2/T3 vs. T4), histological grade (2 vs. 3) and p21 expression (< or = 5% vs. > 5%) were independent prognostic factors for overall survival. CONCLUSION: Further investigation is warranted in patients with muscle-invasive bladder cancer undergoing different types of treatment p21 seems to play an independent prognostic role in these patients, in addition to T category and grade. 相似文献
1000.
We investigate the collective memories of two samples drawn in 1991, one from the former West Germany and one from Yokohama, Japan. In the early 1990s such samples included many members of World War II cohorts and also cohorts born long after that war had ended. We consider the relation of age, conceptualised as birth cohort, to the salience of memories of national and world events that were mentioned as important in response to a quite general open-ended question about the past half-century. The relations are similar across the two countries in so far as external events like World War II might have had similar impacts on each population, while each country is distinctive with regard to events that especially impinged upon it. Hypotheses about the importance of adolescence and early adulthood to the imprinting of memories are generally confirmed, but several types of evidence suggest the need to extend the delimiting ages to earlier than the mid-teens and later than the mid-twenties. Other evidence indicates the desirability of distinguishing between recent events that are the focus of media attention and earlier events that depend more fully on autobiographical memory. 相似文献