全文获取类型
收费全文 | 459150篇 |
免费 | 5893篇 |
国内免费 | 1426篇 |
专业分类
电工技术 | 8011篇 |
综合类 | 452篇 |
化学工业 | 71245篇 |
金属工艺 | 16654篇 |
机械仪表 | 13725篇 |
建筑科学 | 11486篇 |
矿业工程 | 1893篇 |
能源动力 | 11611篇 |
轻工业 | 48045篇 |
水利工程 | 4275篇 |
石油天然气 | 6826篇 |
武器工业 | 37篇 |
无线电 | 53933篇 |
一般工业技术 | 84621篇 |
冶金工业 | 85949篇 |
原子能技术 | 8663篇 |
自动化技术 | 39043篇 |
出版年
2021年 | 3657篇 |
2019年 | 3447篇 |
2018年 | 5672篇 |
2017年 | 5648篇 |
2016年 | 6209篇 |
2015年 | 4116篇 |
2014年 | 7047篇 |
2013年 | 20778篇 |
2012年 | 11913篇 |
2011年 | 16642篇 |
2010年 | 12982篇 |
2009年 | 14564篇 |
2008年 | 15238篇 |
2007年 | 15388篇 |
2006年 | 14016篇 |
2005年 | 12533篇 |
2004年 | 12033篇 |
2003年 | 11766篇 |
2002年 | 11373篇 |
2001年 | 11546篇 |
2000年 | 10811篇 |
1999年 | 11233篇 |
1998年 | 26743篇 |
1997年 | 18753篇 |
1996年 | 14292篇 |
1995年 | 10971篇 |
1994年 | 9688篇 |
1993年 | 9510篇 |
1992年 | 7126篇 |
1991年 | 6639篇 |
1990年 | 6662篇 |
1989年 | 6367篇 |
1988年 | 6150篇 |
1987年 | 5149篇 |
1986年 | 5109篇 |
1985年 | 6104篇 |
1984年 | 5630篇 |
1983年 | 5119篇 |
1982年 | 4780篇 |
1981年 | 4922篇 |
1980年 | 4639篇 |
1979年 | 4411篇 |
1978年 | 4303篇 |
1977年 | 4831篇 |
1976年 | 6176篇 |
1975年 | 3714篇 |
1974年 | 3504篇 |
1973年 | 3711篇 |
1972年 | 2914篇 |
1971年 | 2720篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
91.
Pigmented vulvar lesions were observed in a child during a sexual abuse evaluation. Gross examination of the lesions appeared most consistent with bowenoid papulosis; however, biopsy confirmed the lesions to be pigmented apocrine hamartomas. To our knowledge, these rare and benign tumors have never been described as pigmented, but should be added to the differential diagnosis of pigmented vulvar lesions. 相似文献
92.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel. 相似文献
93.
A case of traumatic extracranial vertebral arterial dissection leading to vertebrobasilar thrombosis and respiratory compromise requiring mechanical ventilation was managed with intraarterial thrombolysis and stenting of the vertebral intimal dissection. In contrast to similar, previously reported cases, this critically ill patient made a full recovery, returning to his job as a secondary school teacher. 相似文献
94.
C Wittekind 《Canadian Metallurgical Quarterly》1996,121(6):435-441
A subpopulation of rabbit polyclonal anti-idiotypic antibody (anti-Id) was previously produced to a murine monoclonal antibody (mAb) (M1875) specific for the bluetongue virus core protein VP7. In this report, mimicry of VP7 by this anti-Id (designated RAb2-A) was functionally analyzed through immunization of Balb/c mice with RAb2-A or purified VP7. Animals immunized with RAb2-A were able to produce an M1875-like Ab3 antibody response with idiotype and epitope specificity resembling that of M1875 without subsequent exposure to the nominal antigen. This conclusion was supported by experiments showing that the RAb2-A-induced Ab3 antibodies (i) reacted specifically with the immunizing anti-Id; (ii) were capable of binding VP7; (iii) inhibited M1875 from binding to VP7; and (iv) inhibited M1875 from binding to RAb2-A. Similarly, mice immunized with purified VP7 also produced antibodies that exhibited characteristics such as idiotype and epitope specificity in common with M1875. No antibody response to VP7 was detected in control groups of mice immunized with either normal rabbit IgG or BHK-21 cell components. Therefore, it can be concluded that rabbit anti-Id RAb-2-A mimics an M1875-defined VP7 epitope sufficiently to function as a surrogate antigen for inducing an anti-bluetongue virus response. 相似文献
95.
D Sternberg A Peled E Shezen O Abramsky W Jiang F Bertolero D Zipori 《Canadian Metallurgical Quarterly》1996,2(1):29-38
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay. 相似文献
96.
W. Lim C. K. Wang 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,370(2-3):568-572
The one-dimensional (1D) position-sensitive superheated-liquid-droplet dosimeter (SLDD) has been fabricated and tested in the laboratory. The 1D SLDD is fabricated from a 9.525-mm OD, 6.35-mm ID, 20-cm long, Plexiglas-walled tube filled with a mixture of superheated-liquid Freon droplets and host medium glycerol. Washer-shaped piezoelectric acoustic transducers are positioned at both ends of the tube; they determine the number and positions of the acoustic events when the superheated-liquid droplets evaporate upon neutron irradiation. The SLDD is irradiated with the 137Cs and 60Co γ-sources, as well as 252Cf neutron source to test for its radiation response and spatial resolution. The SLDD based on the Freon-134a superheated-liquid droplets operating at 20°C and 1 atm is found to be ideal for measuring absorbed neutron dose. This study also proves that the positions of the radiation-induced nucleation acoustic events can be linearly determined from the differences in the transmission times received by the acoustic transducers on the 1D SLDD. The spatial resolution of the neutron depth-dose is 1 mm due the finite response time (1 μs) of the piezoelectric acoustic transducers. 相似文献
97.
The thermal expansion of tellurides of germanium, bismuth, and intermetallic compounds is investigated over the temperature range 293-973 K.Belarusian Agricultural Technical University, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 5, pp. 612–616, May 1994. 相似文献
98.
M.E.W. Eggenkamp V. A. Shvarts R. Blaauwgeers A. Storm R. Jochemsen G. Frossati 《Journal of Low Temperature Physics》1998,110(1-2):299-304
This paper focuses on the hydrodynamics of third sound on a superfluid
3
He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range. 相似文献
99.
Albrecht Jason E.; O'Brien Edward J.; Mason Robert A.; Myers Jerome L. 《Canadian Metallurgical Quarterly》1995,21(2):364
An implicit assumption of several causal reasoning models is that readers adopt the goals of a narrative's protagonist during text comprehension. In apparent violation of this assumption, readers participating in Experiment 1 of the present study drew inferences relevant to a protagonist's goal even when that goal was already satisfied from the perspective of the protagonist. In Experiments 2 and 3, participants were explicitly asked to view the text situation from the point of view of the protagonist. In this case, the goals of the reader and the protagonist should be the same. In these experiments, participants focused on the goals of the protagonist only when those goals had not been satisfied from the perspective of the protagonist. These results are discussed in terms of reader- and character-based perspectives and in terms of text characteristics that cue perspective taking. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
100.
It is now generally recognized that cell growth conditions in nature are often suboptimal compared to controlled conditions provided in the laboratory. Natural stresses like starvation and acidity are generated by cell growth itself. Other stresses like temperature or osmotic shock, or oxygen, are imposed by the environment. It is now clear that defense mechanisms to withstand different stresses must be present in all organisms. The exploration of stress responses in lactic acid bacteria has just begun. Several stress response genes have been revealed through homologies with known genes in other organisms. While stress response genes appear to be highly conserved, however, their regulation may not be. Thus, search of the regulation of stress response in lactic acid bacteria may reveal new regulatory circuits. The first part of this report addresses the available information on stress response in Lactococcus lactis. Acid stress response may be particularly important in lactic acid bacteria, whose growth and transition to stationary phase is accompanied by the production of lactic acid, which results in acidification of the media, arrest of cell multiplication, and possible cell death. The second part of this report will focus on progress made in acid stress response, particularly in L. lactis and on factors which may affect its regulation. Acid tolerance is presently under study in L. lactis. Our results with strain MG1363 show that it survives a lethal challenge at pH 4.0 if adapted briefly (5 to 15 minutes) at a pH between 4.5 and 6.5. Adaptation requires protein synthesis, indicating that acid conditions induce expression of newly synthesized genes. These results show that L. lactis possesses an inducible response to acid stress in exponential phase. To identify possible regulatory genes involved in acid stress response, we determined low pH conditions in which MG1363 is unable to grow, and selected at 37 degrees C for transposition insertional mutants which were able to survive. About thirty mutants resistant to low pH conditions were characterized. The interrupted genes were identified by sequence homology with known genes. One insertion interrupts ahrC, the putative regulator of arginine metabolism; possibly, increased arginine catabolism in the mutant produces metabolites which increase the pH. Several other mutations putatively map at some step in the pathway of (p)ppGpp synthesis. Our results suggest that the stringent response pathway, which is involved in starvation and stationary phase survival, may also be implicated in acid pH tolerance. 相似文献