全文获取类型
收费全文 | 5176篇 |
免费 | 40篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 38篇 |
综合类 | 1篇 |
化学工业 | 348篇 |
金属工艺 | 220篇 |
机械仪表 | 63篇 |
建筑科学 | 98篇 |
矿业工程 | 86篇 |
能源动力 | 75篇 |
轻工业 | 228篇 |
水利工程 | 23篇 |
石油天然气 | 3篇 |
无线电 | 286篇 |
一般工业技术 | 439篇 |
冶金工业 | 2962篇 |
原子能技术 | 34篇 |
自动化技术 | 313篇 |
出版年
2021年 | 40篇 |
2020年 | 23篇 |
2019年 | 31篇 |
2018年 | 28篇 |
2017年 | 29篇 |
2016年 | 40篇 |
2015年 | 27篇 |
2014年 | 48篇 |
2013年 | 155篇 |
2012年 | 72篇 |
2011年 | 106篇 |
2010年 | 93篇 |
2009年 | 104篇 |
2008年 | 90篇 |
2007年 | 110篇 |
2006年 | 107篇 |
2005年 | 67篇 |
2004年 | 68篇 |
2003年 | 68篇 |
2002年 | 57篇 |
2001年 | 57篇 |
2000年 | 68篇 |
1999年 | 127篇 |
1998年 | 980篇 |
1997年 | 549篇 |
1996年 | 366篇 |
1995年 | 194篇 |
1994年 | 185篇 |
1993年 | 216篇 |
1992年 | 59篇 |
1991年 | 63篇 |
1990年 | 42篇 |
1989年 | 58篇 |
1988年 | 34篇 |
1987年 | 48篇 |
1986年 | 47篇 |
1985年 | 49篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 31篇 |
1981年 | 40篇 |
1980年 | 44篇 |
1979年 | 25篇 |
1978年 | 28篇 |
1977年 | 91篇 |
1976年 | 138篇 |
1975年 | 28篇 |
1974年 | 32篇 |
1973年 | 32篇 |
1972年 | 24篇 |
排序方式: 共有5217条查询结果,搜索用时 0 毫秒
101.
102.
Kobeissy FH Sadasivan S Oli MW Robinson G Larner SF Zhang Z Hayes RL Wang KK 《Proteomics. Clinical applications》2008,2(10-11):1467-1483
The rapidly growing field of neuroproteomics has expanded to track global proteomic changes underlying various neurological conditions such as traumatic brain injury (TBI), stroke, and Alzheimer's disease. TBI remains a major health problem with approximately 2?million incidents occurring annually in the United States, yet no affective treatment is available despite several clinical trials. The absence of brain injury diagnostic biomarkers was identified as a significant road-block to therapeutic development for brain injury. Recently, the field of neuroproteomics has undertaken major advances in the area of neurotrauma research, where several candidate markers have been identified and are being evaluated for their efficacy as biological biomarkers in the field of TBI. One scope of this review is to evaluate the current status of TBI biomarker discovery using neuroproteomics techniques, and at what stage we are at in their clinical validation. In addition, we will discuss the need for strengthening the role of systems biology and its application to the field of neuroproteomics due to its integral role in establishing a comprehensive understanding of specific brain disorder and brain function in general. Finally, to achieve true clinical input of these neuroproteomic findings, these putative biomarkers should be validated using preclinical and clinical samples and linked to clinical diagnostic assays including ELISA or other high-throughput assays. 相似文献
103.
Robinson HC Hahn Y 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1991,38(3):305-310
The electrical reflection coefficient r(e) and velocity shift (Deltanu/nu)(e) for grooves has never been formulated. All previous calculations for r(e) and (Deltanu/nu)(e) have used formulas valid for the reflection of a surface acoustic wave (SAW) from an array of conducting strips. However, the discontinuity in electrical boundary conditions leading to these formulas does not exist in groove gratings. A new expression for the electrical reflection coefficient and velocity shift for some material overlays is derived from both the variational principle and perturbation theory. The results for various substrates are compared to show the agreement between the two approaches. The implications of this new formulation for the design of grooved arrays on various materials are discussed, effectively resolving the discrepancy between theory and experiment. 相似文献
104.
We compared development of feline hindlimb collateral circulation after acute occlusion of the terminal aorta by ligation, thrombus formation, and formation of a "closed" aortic loop containing thromboplastin. Collateral circulation development was assessed by aortograms, scintillation scans, neurological signs following occlusion, measurement of hindlimb muscle blood flow, and forelimb and hindlimb temperature. In cats in which aortic occlusion was the result of ligation or thromboplastin in the aortic loop, paralysis was not evident. Aortograms and scintillation scans indicated hindlimb blood flow. Both muscle temperature and blood flow data indicated that the return of blood flow was rapid. The 5th lumbar artery appears to be the origin of the collateral vessels. The mid-zone component is a dorsal and ventral vertebral route and an epaxial muscle route. The reentry components are the 6th or 7th lumbar arteries. The collateral vessels arise from preexisting collateral vessels. Of those cats in which aortic occlusion was the result of a thrombus, all exhibited paralysis. Aortograms, scintillation scans, muscle temperature, and hindlimb blood flow data indicated reduced hindlimb blood flow. The results suggest that the thrombus has an inhibitory effect on the development of collateral circulation. 相似文献
105.
Evaluating water quality data for outliers is a good quality control/quality assessment procedure whether the data are used for monitoring or for modeling. Often water quality data are correlated, e.g., carbonaceous biochemical oxygen demand (CBOD) has some correlation with NH3. Univariate methods for identifying outliers do not consider the correlation between variables and may identify too many data points as outliers or miss observations which have extreme ratios between variables, e.g., a raw wastewater sample with relatively low CBOD but high NH3. Testing for outliers using multivariate methods such as the Mahalanobis distance, Jackknife distance, p-values, or Hadi’s automatically incorporates the correlation or covariance between variables and is fundamentally more correct. Such multivariate methods can better identify potential outliers and avoid eliminating valid data. 相似文献
106.
The effects of serotonergic agonists were examined in intact and spinal fetuses, using an in vivo fetal rat preparation. On Gestational Day 20, fetuses were prepared with a midthoracic or sham spinal transection. Dose-response curves were obtained for quipazine (nonselective 5-hydroxytryptamine [5-HT] agonist; 1.0-10.0 mg/kg), CGS-12066A (5-HT1B agonist; 1.0-30.0 mg/kg), and α-methylserotonin (α-Me-5-HT; 5-HT? agonist; 0.2-15.0 mg/kg). During a 10-min test, each of the agonists (delivered via intraperitoneal injection) influenced fetal behavior: They increased the occurrence of head movements, mouthing, and hindlimb stepping. Quipazine and α-Me-5-HT also promoted hindlimb activity in spinal fetuses. Thus, stimulation of the fetal 5-HT system modulates motor activity at multiple levels of the developing central nervous system. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
Robinson J.A. Liang V.W. Chambers J.A.M. MacKenzie C.L. 《IEEE transactions on systems, man, and cybernetics. Part A, Systems and humans : a publication of the IEEE Systems, Man, and Cybernetics Society》1998,28(2):236-241
The keystroke dynamics of a computer user's login string provide a characteristic pattern that can be used for identity verification. Timing vectors for several hundred login attempts were collected for ten “valid” users and ten “forgers”, and classification analysis was applied to discriminate between them. Three different classifiers were applied, and in each case the key hold times were more effective features for discrimination than the interkey times. Best performance was achieved by an inductive learning classifier using both interkey and hold times. A high rate of typographical errors during login entry is reported. In practice, these are usually corrected errors-that is, they are strings which include backspaces to correct earlier errors-but their presence confounds the use of typing-style analysis as a practical means of securing access to computer systems 相似文献
108.
以公共结构及语言进行应用系统一体化 总被引:1,自引:0,他引:1
介绍了美国佛罗里达电力照明公司对主要业务系统基于公共结构及语言,进行信息集成的工作过程和经验,对企业信息一体化的技术内容和框架结构做了总体介绍,并根据应用实际阐述了公共信息模型的扩展,对其他企业开展信息系统一体化工作具有一定的借鉴作用. 相似文献
109.
The effect of tritium and helium-3 on tensile properties, fracture toughness properties and fracture mechanisms was studied in a modified A-286 alloy, and compared to the effects of hydrogen. The yield strength and work hardening rate showed no sensitivity to helium-3 in the concentration range studied, but the tensile ductility decreased with increased helium concentration. Fracture toughness with tritium plus helium decreased below that obtained with hydrogen alone. Helium-3 caused a decrease in tensile ductility and fracture toughness because it precipitates on and induces failure at grain boundaries. 相似文献
110.
GJ Mancini-Samuelson V Kieweg KM Sabaj S Ghisla MT Stankovich 《Canadian Metallurgical Quarterly》1998,37(41):14605-14612
The modulation of the electron-transfer properties of human medium-chain acyl-CoA dehydrogenase (hwtMCADH) has been studied using wild-type and site-directed mutants by determining their midpoint potentials at various pH values and estimating the involved pKs. The mutants used were E376D, in which the negative charge is retained; E376Q, in which one negative charge (pKa approximately 6. 0) is removed from the active center; E99G, in which a different negative charge (pKa approximately 7.3) also is affected; and E376H (pKa approximately 9.3) in which a positive charge is present. Em for hwtMCADH at pH 7.6 is -0.114 V. Results for the site-directed mutants indicate that loss of a negative charge in the active site causes a +0.033 V potential shift. This is consistent with the assumption that electrostatic interactions (as in the case of flavodoxins) and specific charges are important in the modulation of the electron-transfer properties of this class of dehydrogenases. Specifically, these charge interactions appear to correlate with the positive Em shift observed upon binding of substrate/product couple to MCADH [Lenn, N. D., Stankovich, M. T., and Liu, H. (1990) Biochemistry 29, 3709-3715], which coincides with a pK increase of Glu376-COOH from approximately 6 to 8-9 [Rudik, I., Ghisla, S., and Thorpe, C. (1998) Biochemistry 37, 8437-8445]. From the pH dependence of the midpoint potentials of hwtMCADH two mechanistically important ionizations are estimated. The pKa value of approximately 6.0 is assigned to the catalytic base, Glu376-COOH, in the oxidized enzyme based on comparison with the pH behavior of the E376H mutant, it thus coincides with the pK value recently estimated [Vock, P., Engst, S., Eder, M., and Ghisla, S. (1998) Biochemistry 37, 1848-1860]. The pKa of approximately 7.1 is assigned to Glu376-COOH in reduced hwtMCADH. Comparable values for these pKas for Glu376-COOH in pig kidney MCADH are pKox = 6.5 and pKred = 7.9. The Em measured for K304E-MCADH (a major mutant resulting in a deficiency syndrome) is essentially identical to that of hwtMCADH, indicating that the disordered enzyme has an intact active site. 相似文献