全文获取类型
收费全文 | 593640篇 |
免费 | 7380篇 |
国内免费 | 1036篇 |
专业分类
电工技术 | 10792篇 |
综合类 | 521篇 |
化学工业 | 95791篇 |
金属工艺 | 23861篇 |
机械仪表 | 18978篇 |
建筑科学 | 14220篇 |
矿业工程 | 4384篇 |
能源动力 | 15179篇 |
轻工业 | 47898篇 |
水利工程 | 7171篇 |
石油天然气 | 15105篇 |
武器工业 | 42篇 |
无线电 | 62242篇 |
一般工业技术 | 121035篇 |
冶金工业 | 99710篇 |
原子能技术 | 14854篇 |
自动化技术 | 50273篇 |
出版年
2021年 | 6042篇 |
2020年 | 4434篇 |
2019年 | 5764篇 |
2018年 | 9810篇 |
2017年 | 9997篇 |
2016年 | 10623篇 |
2015年 | 6726篇 |
2014年 | 11114篇 |
2013年 | 27751篇 |
2012年 | 17144篇 |
2011年 | 22832篇 |
2010年 | 18256篇 |
2009年 | 20087篇 |
2008年 | 20522篇 |
2007年 | 20127篇 |
2006年 | 17482篇 |
2005年 | 15758篇 |
2004年 | 14901篇 |
2003年 | 14473篇 |
2002年 | 13983篇 |
2001年 | 13304篇 |
2000年 | 12773篇 |
1999年 | 12471篇 |
1998年 | 28056篇 |
1997年 | 20408篇 |
1996年 | 16000篇 |
1995年 | 12375篇 |
1994年 | 11216篇 |
1993年 | 10979篇 |
1992年 | 8664篇 |
1991年 | 8300篇 |
1990年 | 8265篇 |
1989年 | 8032篇 |
1988年 | 7704篇 |
1987年 | 6990篇 |
1986年 | 6767篇 |
1985年 | 7646篇 |
1984年 | 6924篇 |
1983年 | 6644篇 |
1982年 | 5982篇 |
1981年 | 6076篇 |
1980年 | 5774篇 |
1979年 | 5882篇 |
1978年 | 5803篇 |
1977年 | 6293篇 |
1976年 | 7794篇 |
1975年 | 5222篇 |
1974年 | 4998篇 |
1973年 | 5066篇 |
1972年 | 4334篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
PCR-based procedures in detection and DNA-fingerprinting of Salmonella from samples of animal origin
A. del Cerro S. M. Soto E. Landeras M. A. Gonzlez-Hevia J. A. Guijarro M. C. Mendoza 《Food microbiology》2002,19(6):567
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment. 相似文献
102.
103.
Consideration was given to the decision making procedures based on the fuzzy messages of experts whose preferences on the set of collective decisions can also be fuzzy. 相似文献
104.
105.
A.A. Kendoush 《Nuclear Engineering and Design》1989,110(3):349-360
The paper describes new experimental evidence on the effects of fast neutron irradiation on the nucleation of bubbles in superheated demineralized water during sudden depressurization. The experimental range covered strating pressures of (0.33–6.0) MPa. It was shown that fast neutron irradiation causes significant increases in the bubble formation for specified conditions of pressure, temperature and rate of blowdown. A mechanistic interpretation of the measurements based on a thermodynamic model was included, and comparison was made, in terms of void fraction, with the experimental results. 相似文献
106.
In this paper, the space-vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and to analyze power sources and loads with different connections (delta and wye). This method can also be applied to analyze steady-state (or transient phenomena) and unbalanced sources, including harmonics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits. 相似文献
107.
This paper presents a new method for the generation of a reference voltage for a dynamic voltage restorer (DVR). These voltages, when injected in series with a distribution feeder by a voltage source inverter, can tightly regulate the voltage at the load terminal against imbalance or harmonics in the source side. It is stipulated that the DVR does not supply any real power in the steady state. The reference voltage generation scheme is validated through digital computer simulation studies. 相似文献
108.
R. Sankarasubramanian C. S. Jog T. A. Abinandanan 《Metallurgical and Materials Transactions A》2002,33(4):1083-1090
We examine the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two-dimensional (2-D) systems
under a plane-strain condition with the principal misfit strain components ε*
xx
and ε*
yy
. For systems with cubic elastic moduli, we first show all the shape transitions associated with different values of t=ε*
yy
/ε*
xx
. We also characterize each of these transitions, by studying its dependence on elastic anisotropy and inhomogeneity. For
systems with dilatational misfit (t=1) and those with pure shear misfit (t=−1), the transition is from an equiaxed shape to an elongated shape, resulting in a break in rotational symmetry. For systems
with nondilatational misfit (−1<t<1; t ≠ 0), the transition involves a break in mirror symmetries normal to the x- and y-axes. The transition is continuous in all cases, except when 0<t<1. For systems which allow an invariant line (−1≤t<0), the critical size increases with an increase in the particle stiffness. However, for systems which do not allow an invariant
line (0<t≤1), the critical size first decreases, reaches a minimum, and then starts increasing with increasing particle stiffness;
moreover, the transition is also forbidden when the particle stiffness is greater than a critical value. 相似文献
109.
110.
A new method is described for transferring phase contrast in electron microscopy without artefacts due to oscillations of the phase contrast transfer function (PCTF). This is carried out by in situ image synthesis of two or three exposures transferred with complementary PCTF. The essence of the technique is to use optimized transfer attenuation functions to cut off the negative parts of PCTF. 相似文献