首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   329篇
  免费   11篇
电工技术   5篇
化学工业   93篇
金属工艺   5篇
机械仪表   7篇
建筑科学   8篇
能源动力   6篇
轻工业   28篇
无线电   34篇
一般工业技术   42篇
冶金工业   98篇
原子能技术   7篇
自动化技术   7篇
  2022年   2篇
  2021年   18篇
  2020年   7篇
  2019年   6篇
  2018年   6篇
  2017年   3篇
  2016年   7篇
  2015年   6篇
  2014年   4篇
  2013年   14篇
  2012年   6篇
  2011年   12篇
  2010年   13篇
  2009年   18篇
  2008年   12篇
  2007年   9篇
  2006年   8篇
  2005年   5篇
  2004年   5篇
  2003年   5篇
  2002年   5篇
  2001年   6篇
  2000年   5篇
  1999年   6篇
  1998年   32篇
  1997年   16篇
  1996年   18篇
  1995年   8篇
  1994年   11篇
  1993年   9篇
  1992年   4篇
  1991年   4篇
  1990年   4篇
  1989年   3篇
  1988年   4篇
  1987年   2篇
  1986年   9篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   4篇
  1979年   1篇
  1978年   2篇
  1977年   5篇
  1976年   2篇
  1975年   3篇
  1974年   1篇
  1971年   1篇
  1970年   2篇
排序方式: 共有340条查询结果,搜索用时 31 毫秒
1.
Some reports demonstrated successful genome editing in pigs by one-step zygote microinjection of mRNA of CRISPR/Cas9-related components. Given the relatively long gestation periods and the high cost of housing, the establishment of a single blastocyst-based assay for rapid optimization of the above system is required. As a proof-of-concept, we attempted to disrupt a gene (GGTA1) encoding the α-1,3-galactosyltransferase that synthesizes the α-Gal epitope using parthenogenetically activated porcine oocytes. The lack of α-Gal epitope expression can be monitored by staining with fluorescently labeled isolectin BS-I-B4 (IB4), which binds specifically to the α-Gal epitope. When oocytes were injected with guide RNA specific to GGTA1 together with enhanced green fluorescent protein (EGFP) and human Cas9 mRNAs, 65% (24/37) of the developing blastocysts exhibited green fluorescence, although almost all (96%, 23/24) showed a mosaic fluorescent pattern. Staining with IB4 revealed that the green fluorescent area often had a reduced binding activity to IB4. Of the 16 samples tested, six (five fluorescent and one non-fluorescent blastocysts) had indel mutations, suggesting a correlation between EGFP expression and mutation induction. Furthermore, it is suggested that zygote microinjection of mRNAs might lead to the production of piglets with cells harboring various mutation types.  相似文献   
2.
Hinokitiol, a constituent of the wood of Chamaecyparis taiwanensis, was found to induce differentiation of teratocarcinoma F9 cells. When examined by the agar-overlay method, in which expression of plasminogen activator as a differentiation marker protein was detected, this compound exhibited a dose- and time-dependent induction. Induction of differentiation by hinokitiol occurred irreversibly and required its addition for more than 12h. Among its structure-related compounds tested, tropolone and two colchicine-related compounds exerted potent activities comparable to that of hinokitiol. These findings indicate that free tropolone structure in the molecules plays an essential role in inducing differentiation of F9 cells. Hinokitiol showed a strong inhibitory effect of DNA synthesis in very early stages of culture, suggesting that this effect may be responsible for triggering differentiation of F9 cells.  相似文献   
3.
Swelling degrees of poly(N-vinyl-2-pyrrolidone) (PVP) gel were measured in aqueous salt solutions and in water/organic solvent mixtures to find marked ion- and solvent-specificities. In order to investigate any correlation of those specificities with hydration or solvation of PVP, IR spectra band of the CO group was monitored by means of ATR method both for PVP gel and the relevant solution systems. Dependence of the peak frequency on the swelling ratio suggested that hydration of PVP carbonyl group in deswollen gel systems is different from that in the corresponding solution systems. In the solution systems, PVP carbonyl band showed a high-wavenumber shift for deswollen systems, which can be well correlated with changes in water proton charge through ionic hydration and with Gutmann's acceptor number of organic solvents. In the deswollen gel systems, the CO band showed a low-wavenumber shift, suggesting a strong hydration or doubly hydrated state. This unexpected behavior was interpreted by assuming an intermolecular hydrogen bond of two carbonyl groups intermediated by water molecules.  相似文献   
4.
The effects of lansoprazole given intravenously on gastric mucosal lesions, gastric bleeding and acid secretion were investigated in rats in comparison with those of omeprazole, famotidine and ranitidine. Lansoprazole inhibited the formation of gastric mucosal lesions in rats induced by water-immersion stress or aspirin with ID50 values of 0.26 and 0.99 mg/kg, respectively, and also inhibited gastric bleeding induced by hemorrhagic shock or water-immersion stress with ID50 values of 0.46 and 1.22 mg/kg, respectively. Lansoprazole was more potent than omeprazole, famotidine and ranitidine in inhibiting gastric mucosal lesions and hemorrhagic shock- or stress-induced bleeding. Famotidine and ranitidine showed negligible inhibition of water-immersion stress-induced gastric bleeding. Lansoprazole strongly inhibited water-immersion stress-stimulated acid secretion in rats, whereas famotidine and ranitidine did not show a potent inhibitory effect. These results indicate that lansoprazole exerts prominent inhibitory actions against the formation of gastric mucosal lesions and gastric bleeding by inhibiting acid secretion, and they show that it is superior to histamine H2-receptor antagonists in inhibiting stress-induced gastric bleeding.  相似文献   
5.
A new practical method is proposed which gives a quasi-optimal solution of the dynamic load-dispatching problem formulated by a multiconstraint multiobjective optimization problem. Here, the multiple constraints are rate reserve constraints and power flow ones, and the multiple objectives are fuel cost and CO2 emission. The proposed method is an integration of the following three techniques: (1) “Group Dispatch Scheme,” which is developed by the authors, is used to satisfy a violated constraint easily. This scheme consists of three steps. The first step is to classify all generators into two groups. One is the group which should be more loaded to satisfy the violated constraint, and the other is the should-be less loaded group. The second step is to add some load to the former group, and to subtract the same load from the latter. The third step is to dispatch each group load to each groups generators, respectively; (2) the dynamic load-dispatching algorithm is used which provides, in practical time, quasi-optimal generation trajectories; (3) the conventional weighting parametric method is used to obtain a Pareto optimal solution of multiobjective problems. The effectiveness of the method is clarified by a computer simulation on the actual power system of Kansai Electric Power Company.  相似文献   
6.
BACKGROUND: Cigarette smoking has been shown to increase oxidative DNA damage in human sperm cells. Assessment of the role of cigarette smoking in the etiology of childhood cancer has focused primarily on the effect of maternal smoking. Similar studies in relation to paternal smoking, however, have been inconclusive. Few studies have evaluated the effect of paternal smoking in the preconception period, and most of these could not disentangle the effects of paternal from maternal smoking. PURPOSE: We investigated the relationship of paternal smoking, particularly in the preconception period, with childhood cancer among offspring of the nonsmoking mothers. METHODS: We conducted a population-based, case-control study in Shanghai, People's Republic of China, where the prevalence of smoking is high among men but extremely low among women. The study included 642 childhood cancer case patients (<15 years of age) and their individually matched control subjects. Information concerning parental smoking, alcohol drinking, and other exposures of the index child was obtained by direct interview of both parents of the study subjects. Odds ratios (ORs), derived from conditional logistic regression models, were used to measure the association between paternal smoking and risk of childhood cancers. RESULTS AND CONCLUSIONS: Paternal preconception smoking was related to a significantly elevated risk of childhood cancers, particularly acute leukemia and lymphoma. The risks rose with increasing pack-years of paternal preconception smoking for acute lymphocytic leukemia (ALL) (P for trend = .01), lymphoma (P for trend = .07), and total cancer (P for trend = .006). Compared with children whose fathers had never smoked cigarettes, children whose fathers smoked more than five pack-years prior to their conception had adjusted ORs of 3.8 (95% confidence interval [CI] = 1.3-12.3) for ALL, 4.5 (95% CI = 1.2-16.8) for lymphoma, 2.7 (95% CI = 0.8-9.9) for brain tumors, and 1.7 (95% CI = 1.2-2.5) for all cancers combined. Statistically significant increased risks of cancer were restricted to children under the age of 5 years at diagnosis or those whose fathers had smoked during all of the 5 years prior to conception. IMPLICATIONS: Further studies are needed to confirm the association of paternal smoking with increased risk of cancer in offspring, to clarify the pattern of risks in relation to the timing of cigarette smoking, and to elucidate the biologic mechanism involved in predisposing the offspring to cancer. For example, it may be that paternal smoking induces prezygotic genetic damage that, in turn, acts as the predisposing factor.  相似文献   
7.
The effect of particle agglomeration on sintering has been studied by slipcasting suspensions with pH values ranging from 2 to 11. The rate of densification has been found to depend on the degree of agglomeration. Complete dispersion of alumina primary particles has not been attained through adjustment of pH of suspensions, and agglomerates also remained in the best-dispersed suspension. Elimination of the agglomerates by sedimentation lowered the densification temperature of slip-cast compacts. The grain size-density curve is a function of temperature. High-density and small-grained sintered bodies were obtained by low-temperature long-time firing.  相似文献   
8.
The curing behavior of one-step phenolic molding compounds was studied using results of Rockwell hardness measurements at elevated temperatures with a cone indenter. The curing process was found to advance in a stepwise manner to the final stage of cure at a specific temperature. An explanation for this phenomenon has been attempted by suggesting the alternating occurrence of two types of curing reactions—propagation and crosslinking. After proceeding to some extent of cure, only the propagation reaction can occur through the migration of low molecular resin to the reactive sites of polymer chains. The propagation facilitates the subsequent crosslinking which drastically enhances the hardness of the resin. The results of electrical resistivity measurements and acetone extraction tests were also found to support the occurrence of above phenomenon.  相似文献   
9.
Rockwell hardness measurement at an elevated temperature has been proposed as an evaluation method for the curing characteristics of thermosetting molding compounds. This method is convenient and has a high accuracy over a wide range of curing, Using a cone indenter, the following advantages are brought about: a good correspondence with acetone extraction test, in showing the degree of cure of the internal part of a molding rather than that of the skin layer, and a higher sensitivity in measuring higher degrees of cure. On examining curing behavior of commercial phenolic molding compounds by this method, an inflection point was observed on a plot of the hardness vs log curing time. This critical point has been called “the minimum cure time”, beyond which the molding exhibits good physical properties.  相似文献   
10.
Yttria-ceria-doped tetragonal zirconia (Y,Ce)-TZP)/alumina (Al2O3) composites were fabricated by hot isostatic pressing at 1400° to 1450°C and 196 MPa in an Ar–O2 atmosphere using the fine powders prepared by hydrolysis of ZrOCl2 solution. The composites consisting of 25 wt% Al2O3 and tetragonal zirconia with compositions 4 mol% YO1.5–4 mol% CeO2–ZrO2 and 2.5 mol% YO1.5–5.5 mol% CeO2–ZrO2 exhibited mean fracture strength as high as 2000 MPa and were resistant to phase transformation under saturated water vapor pressure at 180°C (1 MPa). Postsintering hot isostatic pressing of (4Y, 4Ce)-TZP/Al2O3 and (2.5Y, 5.5Ce)-TZP/Al2O3 composites was useful to enhance the phase stability under hydrothermal conditions and strength.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号