全文获取类型
收费全文 | 714204篇 |
免费 | 9925篇 |
国内免费 | 1946篇 |
专业分类
电工技术 | 13125篇 |
综合类 | 704篇 |
化学工业 | 105183篇 |
金属工艺 | 30205篇 |
机械仪表 | 23223篇 |
建筑科学 | 17037篇 |
矿业工程 | 3817篇 |
能源动力 | 18505篇 |
轻工业 | 58962篇 |
水利工程 | 7620篇 |
石油天然气 | 12788篇 |
武器工业 | 43篇 |
无线电 | 80245篇 |
一般工业技术 | 141484篇 |
冶金工业 | 134680篇 |
原子能技术 | 14368篇 |
自动化技术 | 64086篇 |
出版年
2021年 | 5960篇 |
2020年 | 4313篇 |
2019年 | 5557篇 |
2018年 | 15011篇 |
2017年 | 15261篇 |
2016年 | 12954篇 |
2015年 | 7111篇 |
2014年 | 11292篇 |
2013年 | 30448篇 |
2012年 | 19581篇 |
2011年 | 30307篇 |
2010年 | 24890篇 |
2009年 | 26681篇 |
2008年 | 26918篇 |
2007年 | 28033篇 |
2006年 | 19305篇 |
2005年 | 20082篇 |
2004年 | 18334篇 |
2003年 | 17901篇 |
2002年 | 16224篇 |
2001年 | 16014篇 |
2000年 | 15106篇 |
1999年 | 15905篇 |
1998年 | 40675篇 |
1997年 | 28636篇 |
1996年 | 21979篇 |
1995年 | 16350篇 |
1994年 | 14394篇 |
1993年 | 13981篇 |
1992年 | 10210篇 |
1991年 | 9647篇 |
1990年 | 9374篇 |
1989年 | 9147篇 |
1988年 | 8572篇 |
1987年 | 7589篇 |
1986年 | 7346篇 |
1985年 | 8298篇 |
1984年 | 7771篇 |
1983年 | 6969篇 |
1982年 | 6439篇 |
1981年 | 6624篇 |
1980年 | 6215篇 |
1979年 | 6191篇 |
1978年 | 6016篇 |
1977年 | 7113篇 |
1976年 | 9494篇 |
1975年 | 5175篇 |
1974年 | 4876篇 |
1973年 | 4954篇 |
1972年 | 4067篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
M Fern? PO Bendahl A Brisfors K Byman M Ekeberg L Ferraud K Grankvist B Hjalmers A Nilsson G Sellberg L Skoog O St?l I Wingmo 《Canadian Metallurgical Quarterly》1997,36(8):793-798
Estrogen and progesterone receptor analysis results were compared within and between six laboratories in Sweden using frozen breast cancer cytosol samples, and the same technique (enzyme immunoassay, Abbott Laboratories). The concordance in receptor status (positive vs. negative) was excellent (98.4% (571/580)). The discordant results were attributable to values near cut-off (n = 4) or outliers (n = 5), the latter probably being due to analytical errors. One laboratory reported significantly higher ER concentrations than the others; thus caution should be observed when comparing absolute values from different centers. For PgR there were similar differences between the laboratories. However, the intra- and inter-laboratory differences were small compared with the overall variability in ER and PgR content between different samples in a large database. The range of the median intra-laboratory coefficient of variation was 11-23% for ER and 12-19% for PgR, indicating that there is room for improvement in the quality of assay performance. 相似文献
872.
Improved atrial function in bicaval versus standard orthotopic techniques in cardiac transplantation
A Beniaminovitz MT Savoia M Oz M Galantowicz MR Di Tullio S Homma D Mancini 《Canadian Metallurgical Quarterly》1997,80(12):1631-1635
Atrial geometry is preserved in the bicaval technique of cardiac transplantation. Using Doppler echocardiography, we investigated the impact of this technique on preservation of atrial function and found that echocardiographic indexes of atrial function are improved in bicaval cardiac transplants versus the standard orthotopic transplants. 相似文献
873.
Magnetic resonance imaging of the pediatric airway 总被引:1,自引:0,他引:1
FL Rimell AM Shapiro MP Meza S Goldman S Hite B Newman 《Canadian Metallurgical Quarterly》1997,123(9):999-1003
874.
AH Lauber TJ Barrett M Subramaniam M Schuchard TC Spelsberg 《Canadian Metallurgical Quarterly》1997,272(39):24657-24665
The receptor-binding factor (RBF) for the avian oviduct progesterone (Pg) receptor (PR) has previously been shown to be a unique 10-kDa nuclear matrix protein that generates high affinity PR-binding sites on avian DNA. This paper describes the use of Southwestern blot and DNA gel shift analyses with RBF protein to identify a minimal 54-base pair RBF-binding element in the matrix-associated region (MAR) of the Pg-regulated c-myc gene promoter. This element contains a 5'-GC-rich domain and a 3'-AT-rich domain, the latter of which has a homopurine/homopyrimidine structure. The gel shift assays required the generation of an RBF-maltose fusion protein (RBF-MBP), which specifically binds this element and is supershifted when the anti-RBF polyclonal antibody is added. Computer analysis of the full-length amino acid sequence for RBF predicts a DNA-binding motif involving a beta-sheet structure at the N-terminal domain. Southern blot analyses using nuclear matrix DNA suggests that there are dual MAR sites in the c-myc promoter, which flank an intervening domain containing the RBF element. The co-transfection of this MAR sequence, containing the RBF element and cloned into a luciferase reporter vector, together with an RBF expression vector construct, into steroid treated human MCF-7 cells, results in a decrease of the c-myc promoter activity relative to control transfections containing only the parent vector of the RBF expression construct. These data suggest that a unique chromatin/nuclear matrix structure, composed of the RBF-DNA element complex which is flanked by nuclear matrix attachment sites, serves to bind the PR and repress the c-myc promoter. 相似文献
875.
B Hull 《Canadian Metallurgical Quarterly》1997,26(6):18-19
Two hundred and fifteen patients with pulmonary involvement of lobar (regional, segmental) extent were examined. The examination procedure included clinical and laboratory tests, X-ray tomographic study, and computed tomography, bronchoscopy with biopsy, cyto- and histological studies. The nosological diagnosis was established in 96.5% of cases. Differential diagnosis was found to be difficult in 3.5% of cases. 相似文献
876.
Sun J. Gardner M.K. Liu J.W.S. 《IEEE transactions on pattern analysis and machine intelligence》1997,23(10):603-615
The workload of many real time systems can be characterized as a set of preemptable jobs with linear precedence constraints. Typically their execution times are only known to lie within a range of values. In addition, jobs share resources and access to the resources must be synchronized to ensure the integrity of the system. The paper is concerned with the schedulability of such jobs when scheduled on a priority driven basis. It describes three algorithms for computing upper bounds on the completion times of jobs that have arbitrary release times and priorities. The first two are simple but do not yield sufficiently tight bounds, while the last one yields the tightest bounds but has the greatest complexity 相似文献
877.
878.
Phase contrast magnetic resonance imaging (MRI) can provide in vivo myocardial velocity field measurements. These data allow densely spaced material points to be tracked throughout the whole heart cycle using, for example, the Fourier tracking algorithm. To process the tracking results for myocardial deformation and strain quantification, we developed a method that is based on fitting the tracking results to an appropriate local deformation model. We further analyzed the accuracy and precision of the method and provided performance predictions for several local models. In order to validate the method and the theoretical performance analysis, we conducted controlled computer simulations and a phantom study. The results agreed well with expectations. Human heart data were also acquired and analyzed, and provided encouraging results. At the signal-to-noise ratio (SNR) level and spatial resolution expected in clinical settings, the study predicts strain quantification accuracy and precision that may allow the technique to become a practical and powerful noninvasive approach for the study of cardiac function, although clinically acceptable data acquisition strategies for three-dimensional (3-D) data are still a challenge. 相似文献
879.
B Amblard C Assaiante JC Fabre L Mouchnino J Massion 《Canadian Metallurgical Quarterly》1997,114(2):214-225
The ability voluntarily to stabilize the head in space during lateral rhythmic oscillations (0.59+/-0.09 Hz) of the trunk has been investigated during microgravity (microG) and normal gravity (nG) conditions (parabolic flights). Five healthy young subjects, who gave informed consent, were examined. The movements were performed with eyes open or eyes closed, during phases of either microG or nG. The main result was that head orientation with respect to vertical may be stabilized about the roll axis under microG with, as well as without vision, despite the reduction in vestibular afferent and muscle proprioceptive inputs. Moreover, the absence of head stabilization about the yaw axis confirms that the degrees of freedom of the neck can be independently controlled, as was previously reported. These results seem to indicate that voluntary head stabilization does not depend crucially upon static vestibular afferents. Head stabilization in space may in fact be organized on the basis of either dynamic vestibular afferents or a short-term memorized postural body schema. 相似文献
880.
This review is written to evaluate the stereoselectivity in cutaneous hydrolysis and transdermal transport of propranolol prodrug. This discussion will be useful in the development of knowledge about stereoselective cutaneous hydrolysis and its influence on stereoselective transdermal transport of many other chiral prodrugs and drugs. Propranolol prodrugs undergo stereoselective hydrolysis in hairless mouse skin homogenate and in excised skin samples during permeation; the stereoselectivity is markedly biased towards hydrolysis of the (R) isomer. Unlike the liver, the esterase activity of the skin is high in its cytosolic fraction. Most of the lipophilic propranolol prodrugs cause stereoselective permeation across hairless mouse skin. A mechanism of stereoselective permeation of propranolol prodrug across the skin has been proposed, which indicates that the stereoselectivity in permeation is resulted from the stereoselective hydrolysis of lipophilic prodrug during permeation. 相似文献