全文获取类型
收费全文 | 425312篇 |
免费 | 5222篇 |
国内免费 | 1387篇 |
专业分类
电工技术 | 7796篇 |
综合类 | 335篇 |
化学工业 | 64239篇 |
金属工艺 | 16910篇 |
机械仪表 | 13849篇 |
建筑科学 | 9247篇 |
矿业工程 | 2265篇 |
能源动力 | 12047篇 |
轻工业 | 29870篇 |
水利工程 | 4505篇 |
石油天然气 | 8112篇 |
武器工业 | 17篇 |
无线电 | 50905篇 |
一般工业技术 | 86281篇 |
冶金工业 | 79880篇 |
原子能技术 | 9354篇 |
自动化技术 | 36309篇 |
出版年
2022年 | 2685篇 |
2021年 | 4117篇 |
2020年 | 3131篇 |
2019年 | 4050篇 |
2018年 | 6772篇 |
2017年 | 6760篇 |
2016年 | 7275篇 |
2015年 | 4592篇 |
2014年 | 7575篇 |
2013年 | 21327篇 |
2012年 | 12115篇 |
2011年 | 16171篇 |
2010年 | 12874篇 |
2009年 | 14484篇 |
2008年 | 14911篇 |
2007年 | 14754篇 |
2006年 | 13199篇 |
2005年 | 11844篇 |
2004年 | 11116篇 |
2003年 | 11032篇 |
2002年 | 10387篇 |
2001年 | 10109篇 |
2000年 | 9504篇 |
1999年 | 9899篇 |
1998年 | 24943篇 |
1997年 | 17213篇 |
1996年 | 13242篇 |
1995年 | 9947篇 |
1994年 | 8712篇 |
1993年 | 8774篇 |
1992年 | 6375篇 |
1991年 | 5952篇 |
1990年 | 5959篇 |
1989年 | 5598篇 |
1988年 | 5318篇 |
1987年 | 4668篇 |
1986年 | 4583篇 |
1985年 | 5111篇 |
1984年 | 4720篇 |
1983年 | 4292篇 |
1982年 | 3901篇 |
1981年 | 3998篇 |
1980年 | 3695篇 |
1979年 | 3592篇 |
1978年 | 3564篇 |
1977年 | 4015篇 |
1976年 | 5087篇 |
1975年 | 3070篇 |
1974年 | 2843篇 |
1973年 | 2923篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
S. R. Meschyan 《Soil Mechanics and Foundation Engineering》1996,33(1):16-20
A comparison is made between different alternate schemes for determination of the strength of soils possessing rheological
properties on the basis of our own experimental data. An original method is proposed for determination of the ultimate long-term
strength from tests on the conditionally instantaneous failure of soil after preliminary deformation in a creep regime, as
well as from tests in a controlled-deformation regime.
Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 14–18, January–February, 1996. 相似文献
93.
The introduction of high spatial and spectral resolution sensors on-board remote-sensing spacecraft has increased, by orders of magnitude, the data rates which need to be sustained on the down-link or cross-link transmission channels. Since these channels are severely limited in capacity, the need arises to perform on-board compression to reduce the volume of data which would need to be down-linked. This paper discusses the development and refinement of a low complexity lossy spectral/spatial compression method which provides high compression ratios at low levels of distortion. The developed techniques uses pixels in adjacent bands to predict the intensity of pixels in the band being compressed via a simple linear prediction model. This prediction method when combined with a low-distortion discrete cosine transform (DCT) block coding method yields performance comparable to block-adaptive Karhunen-Loeve Transform (KLT)-DCT methods without incurring the complexity penalty of the KLT. The methods' performance suffers under misregistration. A fractional-pixel interpolation enhancement to the basic technique significantly improves the performance in the case of misregistered bands 相似文献
94.
Known examples of the positive influence of electrohydroimpulse treatment on the quality of weld joints of various steels, particularly including an increase in their long-term and cyclic strength and also corrosion resistance, are analyzed. It is shown that in this case there is a reduction in residual macro- and micro-stresses and also a change in the parameters of the dislocation structure of the joint metal in the direction of stabilization of it.Translated from Problemy Prochnosti, No. 4, pp. 119–123, April, 1996. 相似文献
95.
Biryukov S.V. Polevoi V.G. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(6):1160-1170
For pt.I see ibid., vol.43, no.6, pp.1150-9 (1996). An exact solution of the electrostatic problem for calculating the surface charge and electric field distributions in an arbitrary periodic interdigital transducer (IDT) is given using the results of our companion paper. An arbitrary external electric field may be specified along the electrode structure with the unit cell containing one electrode, or several electrodes, of different widths. The potentials of the electrodes that may be specified are also arbitrary. It is shown that in the case without an external field, the solution includes all the known results as special cases. The case of shorted electrodes in the external electric field is investigated in detail. The surface charge and electric field distributions are calculated for a spatially harmonic external field with an arbitrary wavenumber. The results of the calculations are represented graphically for various ratios between the period of the electrode structure and the wavelength of the external field for the case of a unit cell containing one or two electrodes of different widths 相似文献
96.
In a prospective study we found good results concerning postoperative complications (21%), perioperative lethality (3.2%) and lethality during hospital stay (6.5%) after implantation of dynamic hip screws (DHS) in patients with per- and subtrochanteric fractures of the femur. The ability to walk, as well as housing and social care postoperatively and follow-up for at least six months after dismissal demonstrates the importance of these fractures for the elderly. One of three patients needs professional care, 21% at home, 13% in nursing homes. Six months after operation the lethality is nearly 20%, i.e. three times higher than in hospital. These are the essential data for all techniques of osteosynthesis used in patients with these fractures, which could only be documented in prospective studies. 相似文献
97.
98.
Simultaneous determination of six ephedrines in urine sample has been achieved by high performance liquid chromatography on a Lichrospher RP-18 column, using methylamphetamine as internal standard. The 6 ephedrines are well separated in 25 minutes with resolution better than 1.8. This method has high recovery, selectivity and reproducibility, and the linearity is satisfactory from 1.5 micrograms/ml to 25 micrograms/ml with correlation coefficients better than 0.999. 相似文献
99.
PURPOSE: We investigated Sertoli cells in testicular biopsies with carcinoma in situ (CIS) in respect to cytokeratin expression to elucidate the status of Sertoli cell differentiation adjacent to CIS in human testes. Cytokeratin 18 intermediate filaments indicate a state of undifferentiation usually observed in Sertoli cells of prepubertal testes. MATERIALS AND METHODS: 29 testicular biopsies presenting CIS were investigated by means of immunohistochemistry, using a polyclonal antibody against placental-alkaline phosphatase to detect CIS cells and a monoclonal antibody against human cytokeratin 18 to show expression of cytokeratin 18 intermediate filaments in Sertoli cells. RESULTS: All tubules bearing CIS showed positive cytokeratin expression of Sertoli cells if tubules were devoid of normal germ cells. However, a total of 13 specimen revealed CIS cells together with normal germ cells. In the presence of CIS cells together with round or elongated spermatids, adjacent Sertoli cells did not express cytokeratin immunoreactivity. In the case of combined presence of CIS and spermatogonia and primary spermatocytes, Sertoli cells could be found either immunopositive or immunonegative, and were positive in tubules with CIS and spermatogonia only. CONCLUSIONS: Sertoli cells associated with CIS cells undergo a process of dedifferentiation, seen by the re-expression of cytokeratin intermediate filaments. We suggest that this dedifferentiation results in a loss of Sertoli cell function and leads to a cessation of spermatogenic activity. 相似文献
100.