全文获取类型
收费全文 | 198075篇 |
免费 | 2360篇 |
国内免费 | 633篇 |
专业分类
电工技术 | 4088篇 |
综合类 | 124篇 |
化学工业 | 26798篇 |
金属工艺 | 7525篇 |
机械仪表 | 5475篇 |
建筑科学 | 4048篇 |
矿业工程 | 747篇 |
能源动力 | 4677篇 |
轻工业 | 14421篇 |
水利工程 | 1696篇 |
石油天然气 | 2842篇 |
武器工业 | 7篇 |
无线电 | 27396篇 |
一般工业技术 | 37478篇 |
冶金工业 | 45450篇 |
原子能技术 | 3561篇 |
自动化技术 | 14735篇 |
出版年
2021年 | 1255篇 |
2019年 | 1288篇 |
2018年 | 2132篇 |
2017年 | 2108篇 |
2016年 | 2180篇 |
2015年 | 1495篇 |
2014年 | 2632篇 |
2013年 | 7972篇 |
2012年 | 4472篇 |
2011年 | 6131篇 |
2010年 | 4953篇 |
2009年 | 5789篇 |
2008年 | 6169篇 |
2007年 | 6223篇 |
2006年 | 5651篇 |
2005年 | 5322篇 |
2004年 | 5269篇 |
2003年 | 5100篇 |
2002年 | 4913篇 |
2001年 | 5315篇 |
2000年 | 4923篇 |
1999年 | 5448篇 |
1998年 | 15647篇 |
1997年 | 10329篇 |
1996年 | 7943篇 |
1995年 | 5794篇 |
1994年 | 5025篇 |
1993年 | 5035篇 |
1992年 | 3393篇 |
1991年 | 3269篇 |
1990年 | 3222篇 |
1989年 | 3046篇 |
1988年 | 2789篇 |
1987年 | 2239篇 |
1986年 | 2313篇 |
1985年 | 2613篇 |
1984年 | 2316篇 |
1983年 | 2065篇 |
1982年 | 1906篇 |
1981年 | 2051篇 |
1980年 | 1792篇 |
1979年 | 1659篇 |
1978年 | 1658篇 |
1977年 | 2022篇 |
1976年 | 2708篇 |
1975年 | 1422篇 |
1974年 | 1371篇 |
1973年 | 1319篇 |
1972年 | 1126篇 |
1971年 | 956篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
PURPOSE: A bladder injury model was developed using protamine sulfate (PS) and endotoxin lipopolysaccharide (LPS) administered intravesically to female Sprague-Dawley rats. MATERIALS AND METHODS: Experimental and control animals were catheterized and intravesically exposed to PS-LPS, PS, LPS, or phosphate buffered saline. After 4, 24 or 72 hours, rats were sacrificed. Urines and bladder tissues were then obtained. Bladder mucosal permeability was evaluated by measuring 14C-urea uptake 24 hours after injury. Repeated instillations of PS/LPS were also made in another group of rats over a period of 5 weeks to attempt to establish a more serious mucosal injury, possibly reflected by altered staining of the collagen IV component of the urinary basement membrane (UBM). RESULTS: Histological examination of the tissues indicated a maximal inflammatory response in the mucosa 4 hours after instillation of PS/LPS. Neutrophils and macrophages in close proximity to the UBM and intraepithelially could be demonstrated. Bladder permeability was significantly altered (26.9% 14C-urea uptake) in rats assayed 24 hours after the PS/LPS treatment, but not after exposure to PS or LPS alone (11.9 and 17.5%, respectively). Protease activity detected in urines from experimental, but not control, animals coincided with the appearance of inflammatory cells in the lamina propria. Inflammatory injury did not appear to alter the collagen IV staining of the UBM. CONCLUSIONS: This rat bladder injury model is useful for examining controversial issues regarding bladder wall structure-function alterations induced by inflammation and possibly important in the pathobiological mechanisms involved in some patients with interstitial cystitis. 相似文献
992.
I Tohnai Y Goto Y Hayashi M Ueda T Kobayashi M Matsui 《Canadian Metallurgical Quarterly》1996,12(1):37-47
This study investigated the impact of Difficulty Level and Type of Suggestion upon the durability of posthypnotic suggestion over an 8-week period. Seventy-eight highly susceptible subjects selected by both the Harvard Group Scale of Hypnotic Susceptibility: Form A (HGSHS:A) and Stanford Hypnotic Scale of Susceptibility: Form C (SHSS:C) were assigned to six groups (two levels of Difficulty x three Types of Suggestion). S's were tested for posthypnotic suggestion at 1, 3, 6, and 8 weeks. A 2 x 3 x 4 (Difficulty x Suggestion x Time) factorial ANOVA was conducted, with Time treated as a repeated-measure. The outcome variable at each time was either pass or fail for relevant suggestion. We found a significant Time effect, a significant Difficulty effect, and a significant Time x Difficulty interaction. Fewer subjects passed the difficult suggestions than passed the easy suggestions; fewer passed suggestions at a latter time; and the decay in pass rate was more pronounced for the easy suggestion condition, due largely to the higher initial pass rate. Type of Suggestion was not significant, nor were any of the other interactions. Clinical implications were discussed. 相似文献
993.
Papadimitriou V. Dennis T.J. 《Vision, Image and Signal Processing, IEE Proceedings -》1996,143(5):310-314
The construction of an accurate 3-D scene model is a fundamental aspect of any model-based image coding scheme. This article describes the generation of a triangular facet surface representation from the data acquired by a calibrated binocular (stereo) camera system 相似文献
994.
W Eggert-Kruse G Rohr H Kerbel B Schwalbach T Demirakca K Klinga W Tilgen B Runnebaum 《Canadian Metallurgical Quarterly》1996,11(4):784-789
To determine the clinical usefulness of Acridine Orange (AO) staining of spermatozoa as a screening test for the evaluation of semen quality during basic infertility investigation, semen smears from 103 randomly chosen males of subfertile couples were examined. The median duration of infertility was 4.5 years (range 1-15) and the median age was 33 years (range 21-43). The outcome of AO staining ranged from 5 to 81%, with a median of 24%, green fluorescent spermatozoa. Results were not significantly related to the parameters of semen analysis (sperm count, motility, standard morphology, viability, pH and volume, as well as fructose concentration and number of found cells) or to local sperm antibody testing and semen cultures. Fluorescence after AO staining was also not related to sperm functional capacity (evaluated using sperm-mucus interaction tests in vitro and in vivo), or the medical history of the patient. No significant differences in the AO test outcome were seen in patients with explained and unexplained infertility, or with regard to subsequent fertility [with a median value of 21% (range 5-46) green fluorescence in the fertile group, compared with a median value of 28% (range 9-81) green fluorescence in the other men]. The results of this prospective study indicate that under the usual conditions of conception, the AO test is not clinically useful as a screening procedure to determine semen quality during basic infertility investigation. 相似文献
995.
996.
Novolac-type polycondensation of benzaldehyde (B) and pyrogallol (P) has been carried out at 60°C, 75°C and 90°C and at B/P mole ratios of 1.5 and 3.0 using phosphoric acid as catalyst. The reaction follows a 2nd order rate law. By using GC consumption data of benzaldehyde and pyrogallol, kinetic parameters such as the overall rate constants, activation energies (Ea) and logA values are investigated. The activation energies for 1.5 and 3.0 B/P mole ratios are found as 62.3 kJ mol?1 and 56.4 kJ mol?1, respectively. The molecular weights of the resins determined by measuring intrinsic viscosities (25°C, THF) are in the range of 0.03 to 0.07 dL g?1 at various temperatures and B/P mole ratios. 相似文献
997.
Problems of gluing parts made of silicon nitride are considered. The quality of glued joints is estimated. The effects of the composition (the types of binder and filler), the technological parameters (thickness of the joint, roughness of the glued surfaces, porosity of the parts), and the test conditions are considered. The technology for gluing parts made of RBSN and HP parts made of Si3N4 and results of tests of glued joints are described.Translated from Ogneupory, No. 4, pp. 18 – 20, April, 1996. 相似文献
998.
A small TEM-mode dielectric resonator which features a crossing slot on the outer ground conductor plane is presented. The slot, functioning as a short-ended stub line serially inserted into the transmission line, can tune the resonant frequency down. The resonant frequency in a stripline resonator structure is rigorously analyzed by a method based on the spectral domain approach and the equivalent circuit is derived. This resonator is used in a cellular radio VCO with a varactor connected across the slot. The performance of the VCO in the 900-MHZ cellular band is described 相似文献
999.
Ethyl linoleate, ethyl linolenate, ethyl arachidonate and cod liver oil were oxidized with Fenton's reagent. Acrolein, malonaldehyde and 4-hydroxynonenal formed were derivatized to N-methylpyrazoline, N-methylpyrazole and 5-(1'-hydroxyhexyl)-1-methyl-2-pyrazoline with N-methylhydrazine, respectively. The derivatives were simultaneously analysed by gas chromatograph equipped with a fused silica capillary column and a nitrogen-phosphorus detector. The maximum amounts of acrolein (9.7 +/- 2.11 nmol/ml) and malonaldehyde (61.18 +/- 6.51 nmol/ml) were formed from cod liver oil. The highest amount of 4-hydroxynonenal (6.83 +/- 0.53 nmol/ml) was produced from ethyl arathidonate. 相似文献
1000.
Raman spectroscopic studies on photoreactive retinal proteins are comprehensively described, including the basic physics of Raman scattering and illustrative examples of the types of information on the structure and function of the retinal chromophore and its environment which can be obtained from the vibrational Raman spectra. In addition, practical advice and recipes are given which should enable the reader to plan and eventually perform a Raman experiment in a photolabile retinal protein. A dominant role is played by the resonance Raman (RR) experiment with visible laser excitation which selectively probes the retinal chromophore. Much discussion is devoted to bacteriorhodopsin (bR) and its photocycle as a paradigm for a light-induced reaction of a retinal protein. Various time-resolved techniques are described to study the temporal evolution of the bR chromophore by probing RR spectra of intermediate states. Vibrational Raman spectra are interpreted in terms of structure and structural changes of the chromophore. RR spectroscopic studies on halorhodopsin, sensory rhodopsin, and visual pigments are reported, as well as on modified proteins in which retinal analogues are incorporated, and on site-specific mutants. Results of ultraviolet RR experiments which selectively probe the aromatic side chains in the protein backbone are reported. In addition, a promising new technique of near-infrared Raman excitation is discussed. Finally, application of coherent anti-Stokes Raman spectroscopy (CARS) to retinal proteins is reported. 相似文献