全文获取类型
收费全文 | 1807篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 81篇 |
金属工艺 | 9篇 |
机械仪表 | 15篇 |
建筑科学 | 8篇 |
矿业工程 | 3篇 |
能源动力 | 7篇 |
轻工业 | 33篇 |
石油天然气 | 2篇 |
无线电 | 57篇 |
一般工业技术 | 84篇 |
冶金工业 | 1472篇 |
原子能技术 | 6篇 |
自动化技术 | 39篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 16篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 13篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 13篇 |
2013年 | 31篇 |
2012年 | 15篇 |
2011年 | 11篇 |
2010年 | 14篇 |
2009年 | 18篇 |
2008年 | 12篇 |
2007年 | 9篇 |
2006年 | 3篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 12篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 49篇 |
1998年 | 510篇 |
1997年 | 257篇 |
1996年 | 179篇 |
1995年 | 105篇 |
1994年 | 67篇 |
1993年 | 84篇 |
1992年 | 11篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 22篇 |
1988年 | 12篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 36篇 |
1976年 | 57篇 |
1974年 | 3篇 |
排序方式: 共有1818条查询结果,搜索用时 15 毫秒
11.
12.
The human mineralocorticoid receptor of the steroid receptor family contains a modular structure with domain E which is considered to be a hormone binding domain. Recombinant protein approaches enabled us to clearly determine that this domain is also able to interact with F-actin (Kd about 2 microM) and G-actin. Moreover, it was revealed that this mineralocorticoid receptor domain/actin interaction was modulated by specific mineralocorticoid ligands. Agonist (aldosterone) steroid binding almost totally (91%) abolished the interaction with F-actin, while antagonist (progesterone) binding allowed more than 30% of this binding. Steroid modulation of the interaction between domain E and actin indicated that this actin binding is specific and could be essential for cellular mineralocorticoid receptor activity. 相似文献
13.
14.
The beta subunit of human chorionic gonadotropin is potentially encoded by six genes, which can be categorized into two types based on a sequence change at codon 117: GCC for the type I and GAC for the type II genes. We previously showed that, whereas type I genes were exclusively expressed in normal breast tissues, expression of type II genes was associated with malignant transformation (Bellet, D., et al. Cancer Res., 57: 516-523, 1997). We designed a simple and robust test (the CG117 assay) that measures the percentage of type II over both types of chorionic gonadotropin beta mRNAs. Normal breast tissues consistently had a negative CG117 index, whereas cancer breast tissues showed indexes ranging from 0 to 100%. The prognostic significance of the CG117 index was investigated in a series of 99 unilateral invasive primary breast cancer patients with known long-term outcome (median follow-up, 9 years). The CG117 index was positive in 48 (48.5%) of the 99 tumor mRNA samples. The index was not significantly associated with standard prognostic parameters, including clinical and macroscopic tumor size, histopathological grade, and lymph node status or steroid receptor status. Patients with a positive CG117 index in primary tumor mRNA had significantly shorter metastasis-free survival (P = 0.014) and overall survival (P = 0.038) after surgery, compared to patients with a negative index. The prognostic significance of the CG117 index persisted in Cox multivariate regression analysis, both for metastasis-free survival (P = 0.008) and overall survival (P = 0.016), together with lymph node status (P = 0.027 and P = 0.009, respectively). These findings indicate that the CG117 index may contribute to the identification of high-risk breast cancer patients. 相似文献
15.
The level of LamB protein in the outer membrane of Escherichia coli was derepressed in the absence of a known inducer (maltodextrins) under carbohydrate-limiting conditions in chemostats. LamB protein contributed to the ability of the bacteria to remove sugar from glucose-limited chemostats, and well-characterized lamB mutants with reduced stability constants for glucose were less growth competitive under glucose limitation than those with wild-type affinity. In turn, wild-type bacteria were less growth competitive than lamB mutants with enhanced sugar affinity. In contrast to an earlier report, we found that LamB- bacteria were less able to compete in carbohydrate-limited chemostats (with glucose, lactose, arabinose, or glycerol as the carbon and energy sources) when mixed with LamB+ bacteria. The transport Km for [14C]glucose was affected by the presence or affinity of LamB, but only in chemostat-grown bacteria, with their elevated LamB levels. The pattern of expression of LamB and the advantage it confers for growth on low concentrations of carbohydrates are consistent with a wider role in sugar permeation than simply maltosaccharide transport, and hence the well-known maltoporin activity of LamB is but one facet of its role as the general glycoporin of E. coli. A corollary of these findings is that OmpF/OmpC porins, present at high levels in carbon-limited bacteria, do not provide sufficient permeability to sugars or even glycerol to support high growth rates at low concentrations. Hence, the sugar-binding site of LamB protein is an important contributor to the permeability of the outer membrane to carbohydrates in habitats with low extracellular nutrient concentrations. 相似文献
16.
17.
18.
19.
Synthesis and characterization of acidic properties of Al-SBA-15 materials with varying Si/Al ratios
G. Muthu Kumaran Shelu Garg Kapil Soni Manoj Kumar J.K. Gupta L.D. Sharma K.S. Rama Rao G. Murali Dhar 《Microporous and mesoporous materials》2008,114(1-3):103-109
Al-SBA-15 of varying Si/Al ratios in the range 11.4–78.4 was synthesized using tri-block copolymer P123. The calcined materials were examined by XRD, pore size distribution, surface area, 27Al NMR spectroscopy. The acidity and acid strength distribution were studied using microcalorimetric adsorption of NH3. The acidic properties were also examined by cumene cracking reaction as a function of Si/Al ratios. Systematic variation of acidity and activity was observed as a function of Si/Al ratio. The initial heats of NH3 adsorption correlated well with activity indicate that acid sites with ΔH > 100 kJ/mole is responsible for cumene cracking activity. Linear correlations were obtained with total acidity and cumene cracking activities. The tetrahedral aluminum was found to be responsible for the observed acidities and catalytic activities. 相似文献
20.
The expansion of trinucleotide repeat sequences has now been shown to be the underlying cause of at least ten human disorders. Unifying features among these diseases include the unstable behavior of the triplet repeat during germline transmission when the length of the repeat exceeds a critical value. However, the trinucleotide repeat disorders can be divided into two distinct groups. Type I disorders involve the expansion of CAG repeats, which encode an expanded polyglutamine, inserted into the open-reading frame of a gene that is usually quite broadly expressed. Recently, mouse models for type I disorders have been developed and the basis of pathology is under study, both in these models and through biochemical and cell biological approaches. The type II disorders involve repeat expansions in noncoding regions of genes. The mechanisms by which these repeat expansions lead to pathology may be quite diverse. 相似文献