全文获取类型
收费全文 | 683399篇 |
免费 | 7758篇 |
国内免费 | 2568篇 |
专业分类
电工技术 | 12871篇 |
综合类 | 984篇 |
化学工业 | 97256篇 |
金属工艺 | 26764篇 |
机械仪表 | 20621篇 |
建筑科学 | 15667篇 |
矿业工程 | 3305篇 |
能源动力 | 16816篇 |
轻工业 | 54787篇 |
水利工程 | 6849篇 |
石油天然气 | 12148篇 |
武器工业 | 117篇 |
无线电 | 84512篇 |
一般工业技术 | 132801篇 |
冶金工业 | 135635篇 |
原子能技术 | 14930篇 |
自动化技术 | 57662篇 |
出版年
2021年 | 5184篇 |
2019年 | 5038篇 |
2018年 | 8734篇 |
2017年 | 8828篇 |
2016年 | 9326篇 |
2015年 | 6059篇 |
2014年 | 10296篇 |
2013年 | 29354篇 |
2012年 | 16702篇 |
2011年 | 22825篇 |
2010年 | 18125篇 |
2009年 | 20786篇 |
2008年 | 21798篇 |
2007年 | 21820篇 |
2006年 | 19350篇 |
2005年 | 17844篇 |
2004年 | 17565篇 |
2003年 | 17098篇 |
2002年 | 16477篇 |
2001年 | 16692篇 |
2000年 | 15900篇 |
1999年 | 16828篇 |
1998年 | 42755篇 |
1997年 | 29909篇 |
1996年 | 23106篇 |
1995年 | 17581篇 |
1994年 | 15424篇 |
1993年 | 15355篇 |
1992年 | 11248篇 |
1991年 | 10676篇 |
1990年 | 10401篇 |
1989年 | 10084篇 |
1988年 | 9369篇 |
1987年 | 8188篇 |
1986年 | 8187篇 |
1985年 | 9332篇 |
1984年 | 8449篇 |
1983年 | 7709篇 |
1982年 | 7272篇 |
1981年 | 7478篇 |
1980年 | 7169篇 |
1979年 | 6718篇 |
1978年 | 6577篇 |
1977年 | 7722篇 |
1976年 | 10072篇 |
1975年 | 5836篇 |
1974年 | 5641篇 |
1973年 | 5684篇 |
1972年 | 4719篇 |
1971年 | 4228篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
941.
Kobayashi K. Kameyama M. Higuchi T. 《Industrial Electronics, IEEE Transactions on》1997,44(3):418-426
A new token-passing mechanism, priority token passing, which features real-time access and fast detection and recovery of transmission errors, is discussed in detail in comparison with standard token-passing protocols, and its large-scale integration (LSI)-oriented design concept is described. Priority token passing includes only a small performance overhead, due to its switching functions, which can change network topology from ring to broadcast medium. A token-holding node passes the token to another node after determining the successor through priority comparison. Errors occurring during token passing can, thus, be detected and corrected simply and promptly. Priority token passing has a simple hardware implementation, requiring only small additions to the frame control circuitry, and has a small implementation overhead. The priority token-passing protocol and two other important network communication functions, dual ring network reconfiguration and high-level data link control (HDLC) normal response mode-based message transmission, are designed as a single finite-state machine, and implemented into a compact LSI chip. This integrated instrument network (IINET) chip provides complete network communication services and requires only three additional external electronic components for operation 相似文献
942.
943.
We report a case of early Wegener's disease mimicking tuberculosis in a 36 year old man. Lungs are solely affected for 6 months. Unusual appearance of radiographic features with large apical excavations explain the delai for the diagnosis. We discuss morphological features in the lungs and kidney. 相似文献
944.
945.
Effect of oral administration of fenvalerate, a pyrethroid insecticide was studied in different behavioral paradigms in mice. Fenvalerate at 15, 30 and 45 mg/kg dose increased start latency, decreased ambulation and rearing in open-field, increased immobility in tail-suspension test and attenuated haloperidol-induced catalepsy in a dose-dependent manner. The time-course of data shows that these effects of fenvalerate may sustain up to several hours of its oral administration. The study indicates that pyrethroids can cause adverse behavioral effects even after a very low-level exposure. Although, it is difficult to extrapolate these findings directly to behavioral changes in man, they indicate that subtle behavioral dysfunction also occur in humans at exposures which do not cause acute toxicity. 相似文献
946.
Since its introduction into the analytical laboratory, CE has had to prove that it was capable of generating results comparable to HPLC or GC techniques in the six areas (specificity, precision, accuracy, linearity, ruggedness, and range) typically required of validated methods intended for submission to governmental agencies. This paper will showcase the development and validation of two analytical methods: one for specific identification of HEPES (N-[2-hydroxyethyl]piperazine-N'-[2-ethane sulfonic acid]) and the other to quantitate millimolar concentrations of tris (tris[hydroxymethyl]aminomethane) in high electrolyte solutions. Utilizing neutral markers and internal standards, results for HEPES demonstrate that migration time reproducibility, expressed as %RSD of 2% or less on a variety of capillaries, is obtainable. Additionally, for quantitation of tris, the values obtained for accuracy (%relative mean bias), precision (%RSD), and linearity (r2) over multiple days and capillaries meet the rigorous standards we require of HPLC or GC methods. 相似文献
947.
The dissociation pK values of the representative loop diuretics furosemide, bumetanide and ethacrynic acid in 10, 30, 40, 50 and 70% (w/w) acetonitrile-water mixtures at 298.15 K were determined, according to the rules and procedures endorsed by IUPAC. The variation in pK values over the whole composition range studied can be explained by tacking into account the preferential solvation of ionizable substances in acetonitrile-water mixtures. With a view to determining the pK values of the loop diuretics studied in any of the binary solvent acetonitrile-water mixtures, correlations of pK values and different bulk properties of the solvent were examined, and the linear solvation energy relationships method, LSER, has been applied. The pK values were then correlated with the pi*, alpha and beta solvatochromic parameters of acetonitrile-water mixtures. The resulting equations allowed us to calculate pK values for the loop diuretics in any acetonitrile-water mixture up to 70% (w/w) acetonitrile. 相似文献
948.
The hypothesis of Geisler (Brain Res. 212 (1981) 198-201), in which the different spontaneous-rate classes of primary auditory neurons were accounted for by the different sizes of uniquantal EPSPs relative to the gap between resting membrane and threshold potentials, was represented with an expanded model which included relative refractory effects. The spike rates generated by the expanded model, when plotted vs. estimated sound level, are qualitatively similar to those of experimentally obtained rate-level curves. The hypothesis is also consistent with recent ultrastructural data which suggest that average quantal-release rates for any particular primary auditory neuron are inversely related to its spontaneous rate. The model's recovery processes following spike generation (hazard functions) are also similar to those observed experimentally. 相似文献
949.
950.
T Ohnishi T Yano S Nakano S Jinnouchi S Nagamachi LI Flores H Nakahara K Watanabe 《Canadian Metallurgical Quarterly》1997,38(9):1463-1467
We compared the acetazolamide challenge test using 99mTc-ECD SPECT and 123I-IMP SPECT images in patients with chronic occlusive cerebrovascular disease. We also evaluated the usefulness of linearization correction for acetazolamide challenge test of 99mTc-ECD SPECT. METHODS: Twenty patients with unilateral chronic occlusive cerebrovascular disease (10 patients had middle cerebral arterial lesion and 10 had internal carotid lesion) were included in the study. Split-dose (a dose fractioning was 1:2), and sequential SPECT technique was used for 99mTc-ECD SPECT studies while only acetazolamide challenge test studies for 123I-IMP SPECT were performed. Permeability surface area product model (PS model) and back-diffusion model (Lassen's correction) were used for linearization correction of acetazolamide challenge with 99mTc-ECD SPECT. RESULTS: Six of 16 patients with reduced vasodilatory capacity in 123I-IMP SPECT were underestimated by 99mTc-ECD SPECT acetazolamide challenge test. Relative ECD uptake normalized by cerebellar uptake compared with IMP uptake showed a nonlinear relationship, indicating relatively less uptake in high flow range. The underestimations of limited vasodilatory capacity observed in 99mTc-ECD SPECT without linearization correction was modified by linearization algorithm. However, the effect of correction based on PS model was superior than that of Lassen's correction. The corrected 99mTc-ECD uptake ratio, based on PS model, and IMP uptake ratio demonstrated a better linear relationship than that of Lassen's correction. CONCLUSION: Technetium-99m ECD SPECT corrected based on the PS model is a better method of linearization for evaluating cerebrovascular reserve using acetazolamide challenge. 相似文献