全文获取类型
收费全文 | 845837篇 |
免费 | 12564篇 |
国内免费 | 2552篇 |
专业分类
电工技术 | 15129篇 |
综合类 | 916篇 |
化学工业 | 129147篇 |
金属工艺 | 31246篇 |
机械仪表 | 24671篇 |
建筑科学 | 21052篇 |
矿业工程 | 3785篇 |
能源动力 | 22660篇 |
轻工业 | 78467篇 |
水利工程 | 8166篇 |
石油天然气 | 14122篇 |
武器工业 | 72篇 |
无线电 | 96509篇 |
一般工业技术 | 158980篇 |
冶金工业 | 166649篇 |
原子能技术 | 16210篇 |
自动化技术 | 73172篇 |
出版年
2021年 | 7295篇 |
2020年 | 5344篇 |
2019年 | 6793篇 |
2018年 | 11363篇 |
2017年 | 11189篇 |
2016年 | 12032篇 |
2015年 | 8249篇 |
2014年 | 13750篇 |
2013年 | 38968篇 |
2012年 | 22212篇 |
2011年 | 30954篇 |
2010年 | 24381篇 |
2009年 | 27331篇 |
2008年 | 28201篇 |
2007年 | 27980篇 |
2006年 | 24928篇 |
2005年 | 22644篇 |
2004年 | 21745篇 |
2003年 | 21393篇 |
2002年 | 20450篇 |
2001年 | 20427篇 |
2000年 | 19140篇 |
1999年 | 20237篇 |
1998年 | 51165篇 |
1997年 | 35826篇 |
1996年 | 27397篇 |
1995年 | 20760篇 |
1994年 | 18168篇 |
1993年 | 17877篇 |
1992年 | 12953篇 |
1991年 | 12096篇 |
1990年 | 12075篇 |
1989年 | 11625篇 |
1988年 | 11054篇 |
1987年 | 9601篇 |
1986年 | 9467篇 |
1985年 | 10903篇 |
1984年 | 10144篇 |
1983年 | 9105篇 |
1982年 | 8553篇 |
1981年 | 8759篇 |
1980年 | 8272篇 |
1979年 | 7950篇 |
1978年 | 7682篇 |
1977年 | 9069篇 |
1976年 | 11861篇 |
1975年 | 6681篇 |
1974年 | 6284篇 |
1973年 | 6537篇 |
1972年 | 5275篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
N Manabe Y Imai H Ohno Y Takahagi M Sugimoto H Miyamoto 《Canadian Metallurgical Quarterly》1996,52(7):647-651
The porcine antral follicles, 3-6 mm in diameter, were dissected from the ovaries of mature pigs, and then granulosa and cumulus cells were isolated from each follicle. In atretic follicles, high activity of neutral Ca2+/Mg2+-dependent endonuclease and DNA ladder formation, estimated by electrophoresis, were noted in granulosa cells but not in cumulus cells. Extremely low activity of the endonuclease and no DNA ladder formation were observed in both types of cells obtained from healthy follicles. Moreover, apoptotic cells were observed histochemically among granulosa cells only. A good correlation (r = 0.987) between the endonuclease activity of granulosa cells and the progesterone/estradiol ratio of follicular fluid in each follicle was found. These results suggest that apoptosis occurs in granulosa cells but not cumulus cells in the atretic antral follicles in pigs. 相似文献
912.
JF Favarel-Garrigues F Sztark ME Petitjean M Thico?pé P Lassié P Dabadie 《Canadian Metallurgical Quarterly》1996,82(2):312-316
Protective immunity against infection with Mycobacterium tuberculosis is imparted by T cells rather than antibodies, but B cells can play a role as antigen-presenting cells and in granuloma formation. We re-evaluated the role of B cells in the course of tuberculous infection in mu-chain knock-out (Ig-) mice. Surprisingly, the organs of M. tuberculosis-infected Ig- mice were found to have three- to eight-fold elevated counts of viable bacilli compared with normal littermates at 3-6 weeks post-infection. Splenic interferon-gamma responses to whole antigen were unimpaired, whilst proliferation to certain mycobacterial peptides was found to be diminished. However, bacille Calmette-Guérin (BCG) vaccination significantly reduced the infection in Ig- mice. The mechanisms by which B cells can influence primary tuberculous infection need further study. 相似文献
913.
M Camilleri 《Canadian Metallurgical Quarterly》1996,25(2):361-378
Gastrointestinal symptoms are often encountered in patients with diabetes mellitus. Symptoms may arise in any region of the alimentary tract; common symptoms are heartburn, nausea, vomiting, diarrhea, constipation, fecal incontinence, and abdominal pain. This article reviews practical approaches to the identification of the pathophysiologic mechanisms involved in diabetic enteropathies and their complications and briefly outlines strategies to treat these symptoms. Particular emphasis is placed on applied physiologic tests and the choice of pharmacotherapy (e.g., cisapride, erythromycin, or octeotide). The current role of pancreatic transplantations also is briefly reviewed. 相似文献
914.
Manku T. McGregor J.M. Nathan A. Roulston D.J. Noel J.-P. Houghton D.C. 《Electron Devices, IEEE Transactions on》1993,40(11):1990-1996
Results of the drift hole mobility in strained and unstrained SiGe alloys are reported for Ge fractions varying from 0 to 30% and doping levels of 1015-1019 cm-3. The mobilities are calculated taking into account acoustic, optical, alloy, and ionized-impurity scattering. The mobilities are then compared with experimental results for a boron doping concentration of 2×1019 cm-3. Good agreement between experimental and theoretical values is obtained. The results show an increase in the mobility relative to that of silicon 相似文献
915.
Cellulose diacetate and triacetate films 6–55 µm thick with a total porosity of 0.8–2% were prepared by pouring a solution on an immobile surface and by calendering. Sorption of H2S and CO2 gases and acetone vapors on these films was investigated in static and dynamic conditions. It was shown that films 6–10 µm thick prepared by calendering should be used for purification of air from H2S and CO2 and films 15–20 µm thick prepared by pouring should be used for removal of acetone vapors.Engels Institute of Technology, Saratov State University. Translated from Khimicheskie Volokna, No. 6, pp. 44–46, November–December, 1995. 相似文献
916.
Suboptimal parallel schemes for the acquisition of spreading sequences in chip-asynchronous spread-spectrum systems are considered. These acquisition schemes estimate the unknown delay of the received signal with respect to a locally generated spreading code. Two schemes are presented which are considerably easier to implement than the optimal estimator. An analytical expression is given for the error probability of the simpler of the two schemes, and it is shown that the average error probability of this scheme decreases exponentially with the signal-to-noise ratio. Numerical results show that the performance of both suboptimal estimators is comparable to that of the optimal estimator 相似文献
917.
918.
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
919.
Modeling ion implantation of HgCdTe 总被引:2,自引:0,他引:2
H. G. Robinson D. H. Mao B. L. Williams S. Holander-Gleixner J. E. Yu C. R. Helms 《Journal of Electronic Materials》1996,25(8):1336-1340
Ion implantation of boron is used to create n on p photodiodes in vacancy-doped mercury cadmium telluride (MC.T). The junction
is formed by Hg interstitials from the implant damage region diffusing into the MC.T and annihilating Hg vacancies. The resultant
doping profile is n+/n-/p, where the n+ region is near the surface and roughly coincides with the implant damage, the n- region is where Hg vacancies have been annihilated revealing a residual grown-in donor, and the p region remains doped by
Hg vacancy double acceptors. We have recently developed a new process modeling tool for simulating junction formation in MC.T
by ion implantation. The interstitial source in the damage region is represented by stored interstitials whose distribution
depends on the implant dose. These interstitials are released into the bulk at a constant, user defined rate. Once released,
they diffuse away from the damage region and annihilate any Hg vacancies they encounter. In this paper, we present results
of simulations using this tool and show how it can be used to quantitatively analyze the effects of variations in processing
conditions, including implant dose, annealing temperature, and doping background. 相似文献
920.
Lead content of rice collected from various areas in the world 总被引:1,自引:0,他引:1
ZW Zhang CS Moon T Watanabe S Shimbo M Ikeda 《Canadian Metallurgical Quarterly》1996,191(1-2):169-175
Rice samples consumed by local populations were collected between 1990 and 1995 in 17 areas in the world, mostly from Asia (10 areas), but also from 7 areas outside of Asia. In total, 1528 samples were obtained (about one half from Japan) and were analyzed for lead (Pb) by electrothermal atomic absorption spectrometry. When the Pb contents in rice samples were classified into 10 areas in Asia, the highest and the lowest geometric means (GMs) were for Indonesia (38 ng/g) and Australia (2 ng/g), respectively. Among 7 regions outside Asia, the GM was highest for Spain (58 ng/g) and the lowest for the USA. (3 ng/g). Moreover, inter-regional differences were significant, when more than 100 samples from one area were divided into 3-9 regions and GMs for regions were compared. There was a marked difference in Pb contents in rice by areas and regions in the world. Nevertheless, comparison by area of the present results with those reported in literature show that there has been no substantial reduction in Pb in rice in the past decade either in Japan or elsewhere in the world. 相似文献