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   2302篇
  免费   15篇
  国内免费   2篇
电工技术   18篇
综合类   1篇
化学工业   131篇
金属工艺   22篇
机械仪表   46篇
建筑科学   48篇
矿业工程   2篇
能源动力   20篇
轻工业   74篇
水利工程   1篇
石油天然气   1篇
无线电   146篇
一般工业技术   152篇
冶金工业   1576篇
原子能技术   7篇
自动化技术   74篇
  2022年   7篇
  2021年   3篇
  2020年   15篇
  2019年   12篇
  2018年   13篇
  2017年   14篇
  2016年   16篇
  2015年   13篇
  2014年   26篇
  2013年   37篇
  2012年   19篇
  2011年   36篇
  2010年   25篇
  2009年   39篇
  2008年   40篇
  2007年   33篇
  2006年   18篇
  2005年   26篇
  2004年   42篇
  2003年   31篇
  2002年   35篇
  2001年   34篇
  2000年   23篇
  1999年   65篇
  1998年   477篇
  1997年   301篇
  1996年   193篇
  1995年   110篇
  1994年   100篇
  1993年   100篇
  1992年   20篇
  1991年   24篇
  1990年   16篇
  1989年   21篇
  1988年   28篇
  1987年   18篇
  1986年   15篇
  1985年   17篇
  1984年   4篇
  1983年   11篇
  1982年   14篇
  1981年   26篇
  1980年   21篇
  1979年   6篇
  1978年   9篇
  1977年   56篇
  1976年   91篇
  1975年   4篇
  1973年   3篇
  1955年   3篇
排序方式: 共有2319条查询结果,搜索用时 15 毫秒
91.
The ability of lonidamine (LND), an energolytic derivative of indazole-carboxylic acid, to modulate the cytotoxic activity of cisplatin (CDDP) and epidoxorubicin (EPI), singly or in combination, was investigated in two human breast cancer cell lines (MCF7 and T47D). A 72-hr post-incubation with a non-cytotoxic concentration of LND (75 microM) increased the activity of a 1-hr CDDP treatment as well as that of a 1 to 16-hr EPI treatment. A different pattern of interaction among the drugs and modulator was observed as a function of the sequence of drug treatment. Specifically, supra-additive or additive effects of the combination were obtained in the two cell lines according to the different treatment schemes. In particular, the maximum potentiation was observed in MCF7 cells simultaneously exposed to CDDP, EPI and LND for 1 hr and then post-incubated with LND for 72 hr, and in T47 first exposed to EPI and LND, then to CDDP and LND, and finally post-incubated with LND. Flow cytometric analysis of MCF7 cell distribution in the different cycle phases showed that combined treatment with EPI/CDDP/LND was able to stabilize cell cycle perturbations (mainly G2M accumulation) induced by individual agents. The ability of LND to potentiate CDDP and EPI cytotoxicity, and the consideration that LND causes side effects different from those caused by alkylating agents and anthracyclines, make this compound an attractive candidate for multidrug combination therapy in breast cancer.  相似文献   
92.
93.
Twenty-six hop bitter resins, some hitherto not investigated, were tested for antimicrobial activities. Gram-positive bacteria were much more sensitive than Gram-negative ones. The inhibitory effect against Bacillus subtilis 168 was measured by several methods and the general rule could be established that the antibiotic properties are mainly dependent on the hydrophobic parts of the molecules. Thus the acyl-lupuphenones (2-acyl-3,5-4,4',6-tri(3-methyl-2-butenyl)-cyclohexane-triones (1, 3, 5) having three prenyl and one acyl side chain are the most active substances. Their minimum inhibitory concentration (MIC) increases from the capro (0.5 muM) to the aceto derivative (11 muM). Any substitution with hydrophilic functions or loss of hydrophobic groups causes reductions in biological activity. This is most evident with the corresponding acyl-phloroglucine precursors (2-acyl-1,3,5-trihydroxybenzenes) which lack the three prenyl side chains (MIC, 110 to 5050 muM respectively). Conversion of the central six-membered ring structure into a five-membered one results in additional losses of antimicrobial activity. These findings support the proposal that the lipophilic region of the cell membrane represents the target site for the hop bitter resins.  相似文献   
94.
95.
96.
Extended measurements and theory on the recently developed monolithic wavelength demultiplexer consisting of voltage-tunable superlattice p-i-n photodetectors in a waveguide confirmation are discussed. It is shown that the device is able to demultiplex and detect two optical signals with a wavelength separation of 20 nm directly into different electrical channels at a data rate of 1 Gb/s and with a crosstalk attenuation varying between 20 and 28 dB, depending on the polarization. The minimum acceptable crosstalk attenuation at a data rate of 100 Mb/s is determined to be 10 dB. The feasibility of using the device as a polarization angle sensor for linearly polarized light is also demonstrated. A theory for the emission of photogenerated carriers out of the quantum wells is included, since this is potentially a speed limiting mechanism in these detectors. It is shown that a theory of thermally assisted tunneling by polar optical phonon interaction is able to predict emission times consistent with the observed temporal response  相似文献   
97.
Cerebral palsy has an incidence of approximately 1/500 births, although this varies between different ethnic groups. Genetic forms of the disease account for approximately 1%-2% of cases in most countries but contribute a larger proportion in populations with extensive inbreeding. We have clinically characterized consanguineous families with multiple children affected by symmetrical spastic cerebral palsy, to locate recessive genes responsible for this condition. The eight families studied were identified from databases of patients in different regions of the United Kingdom. After ascertainment and clinical assessment, we performed a genomewide search for linkage, using 290 polymorphic DNA markers. In three families, a region of homozygosity at chromosome 2q24-q25 was identified between the markers D2S124 and D2S148. The largest family gave a maximum LOD score of 3.0, by multipoint analysis (HOMOZ). The maximum combined multipoint LOD score for the three families was 5.75. The minimum region of homozygosity is approximately 5 cM between the markers D2S124 and D2S2284. We have shown that a proportion of autosomal recessive symmetrical spastic cerebral palsy maps to chromosome 2q24-25. The identification of genes involved in the etiology of cerebral palsy may lead to improved management of this clinically intractable condition.  相似文献   
98.
ɛ ′) and relative loss factor (ɛ′′) give information on how the microwaves can penetrate into the wood object and of possible thermal gradient effects on the wood during modification. This investigation shows that microwave energy effectively heats the acetic anhydride used for modification by acetylation and that the power penetration depth (d p) of the microwaves is about 10 cm in acetic anhydride impregnated wood. The relative permittivity and the relative loss factor were found to decrease with increasing temperature, which indicates that the energy absorption will preferably be directed to less heated parts of the wood object. This will promote a more uniform heat distribution, and, accordingly, a more uniform acetylation of the wood.
d p) für das getr?nkte Holz etwa 10 cm betr?gt. Dielektrizit?tskonstante und Verlustfaktor nehmen mit steigender Temperatur ab; d.h. die Energieaufnahme wird vorzugsweise zu den weniger erhitzten Teilen des Holzes gelenkt. Das wiederum f?rdert eine gleichf?rmige Acetylierung des Holzes.
  相似文献   
99.
Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae possess the ability to cleave human IgA1 antibodies, and all successfully colonize and occasionally invade the human upper respiratory tract. N. meningitidis invades the bloodstream after a period of nasopharyngeal colonization. We directly compared levels of IgA1 protease activity in strains (n=52) derived from the cerebrospinal fluid or blood of patients with meningococcal disease with strains of N. meningitidis obtained from asymptomatic carriers (n=25). IgA1 protease activity was determined by a sensitive semiquantitative ELISA assay. Levels of IgA1 protease activity were significantly higher (P<0.0001) in strains associated with invasive meningococcal disease (98% with detectable activity, mean = 580 mU) than with those obtained from asymptomatic carriers (76% with detectable activity, mean = 280 mU). Despite marked variation in enzyme activity, almost all strains (96%) possessed the gene for IgA1 protease. Given the panmictic population structure of the bacterial isolates investigated, these data, obtained from two groups infected with N. meningitidis, but with markedly different clinical outcomes, provide the first quantitative evidence that IgA1 protease activity is a virulence determinant that contributes to the pathogenic phenotype, and suggest IgA1 protease as a potential target for prophylaxis.  相似文献   
100.
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