全文获取类型
收费全文 | 781105篇 |
免费 | 9561篇 |
国内免费 | 1723篇 |
专业分类
电工技术 | 14610篇 |
综合类 | 683篇 |
化学工业 | 118659篇 |
金属工艺 | 33546篇 |
机械仪表 | 25721篇 |
建筑科学 | 18119篇 |
矿业工程 | 5110篇 |
能源动力 | 20062篇 |
轻工业 | 61136篇 |
水利工程 | 8952篇 |
石油天然气 | 16798篇 |
武器工业 | 49篇 |
无线电 | 88071篇 |
一般工业技术 | 159648篇 |
冶金工业 | 135224篇 |
原子能技术 | 17823篇 |
自动化技术 | 68178篇 |
出版年
2021年 | 6895篇 |
2020年 | 5088篇 |
2019年 | 6517篇 |
2018年 | 15193篇 |
2017年 | 15480篇 |
2016年 | 14359篇 |
2015年 | 7731篇 |
2014年 | 12884篇 |
2013年 | 34276篇 |
2012年 | 21190篇 |
2011年 | 31101篇 |
2010年 | 25637篇 |
2009年 | 27543篇 |
2008年 | 28257篇 |
2007年 | 29122篇 |
2006年 | 21446篇 |
2005年 | 20969篇 |
2004年 | 19472篇 |
2003年 | 19247篇 |
2002年 | 17919篇 |
2001年 | 17492篇 |
2000年 | 16591篇 |
1999年 | 16688篇 |
1998年 | 40147篇 |
1997年 | 28596篇 |
1996年 | 22265篇 |
1995年 | 16938篇 |
1994年 | 15294篇 |
1993年 | 15039篇 |
1992年 | 11290篇 |
1991年 | 11014篇 |
1990年 | 10774篇 |
1989年 | 10349篇 |
1988年 | 10022篇 |
1987年 | 8912篇 |
1986年 | 8686篇 |
1985年 | 9751篇 |
1984年 | 8810篇 |
1983年 | 8506篇 |
1982年 | 7703篇 |
1981年 | 7768篇 |
1980年 | 7483篇 |
1979年 | 7369篇 |
1978年 | 7136篇 |
1977年 | 8147篇 |
1976年 | 10483篇 |
1975年 | 6345篇 |
1974年 | 6141篇 |
1973年 | 6116篇 |
1972年 | 5306篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
902.
A case of endometrioid carcinoma arising from endometriosis of the sigmoid colon is reported. The patient had been treated with unopposed continuous estrogen injection for twenty years after bilateral salpingo-oophorectomy because of severe endometriosis. The pathology, pertinent literature and implications of the present case are discussed. 相似文献
903.
904.
A Trattner Z Reizis M David A Ingber J Hagler M Sandbank 《Canadian Metallurgical Quarterly》1993,129(5):590-593
Interferon alpha-2a, which has antineoplastic, antiviral, immunomodulatory, and antiangiogenic effects, was evaluated in a prospective study, treating 10 lesions of patients with classical Kaposi's sarcoma. Ten patients received injections of interferon alpha-2a intralesionally in a dose of 3 million units three times weekly for 4 weeks, and in a variable dose for 4 more weeks. Two of the patients had a complete response, and in one of these, distant lesions also responded. Seven had a partial response, and one did not respond. The treatment was generally well tolerated. The results of our study support the use of interferon in the therapy of classical Kaposi's sarcoma, although it would appear that to achieve maximum efficacy, a longer period of treatment is needed. 相似文献
905.
906.
LW Seymour H Soyez A De Marre MA Shoaibi EH Schacht 《Canadian Metallurgical Quarterly》1996,11(5):351-365
Prodrugs of mitomycin C (MMC) based on soluble poly-[N-(2-hydroxyethyl)-L-glutamine] (pHEG) polymers have been evaluated as tumour-targeted drugs. These materials are designed to exploit the enhanced permeability of tumour vasculature, combining a passive tumour tropism with decreased systemic liberation of free MMC. A tri- or tetrapeptide linkage (e.g. Gly-Phe-Ala-Leu) between pHEG and the aziridine nitrogen of MMC can combine good hydrolytic stability with rapid cleavage by lysosomal enzymes, releasing free MMC. The conjugates showed decreased systemic toxicity and could be administered to mice at a total MMC dose of 15 mg/kg i.v., compared with just 6 mg/kg for free MMC. Conjugates also showed better activity against animal models of established tumours, achieving up to 77% increased life span (ILS) against solid P388 leukaemia, compared with only 23% for free MMC, and up to 121% ILS against solid C26 colorectal carcinoma, compared with no activity for the free drug. Improving the therapeutic index of anticancer drugs by combining tumour tropism with decreased systemic toxicity is a versatile approach that should produce a new generation of improved anticancer agents. 相似文献
907.
Manku T. McGregor J.M. Nathan A. Roulston D.J. Noel J.-P. Houghton D.C. 《Electron Devices, IEEE Transactions on》1993,40(11):1990-1996
Results of the drift hole mobility in strained and unstrained SiGe alloys are reported for Ge fractions varying from 0 to 30% and doping levels of 1015-1019 cm-3. The mobilities are calculated taking into account acoustic, optical, alloy, and ionized-impurity scattering. The mobilities are then compared with experimental results for a boron doping concentration of 2×1019 cm-3. Good agreement between experimental and theoretical values is obtained. The results show an increase in the mobility relative to that of silicon 相似文献
908.
PURPOSE: To assess the role postoperative mydriatics play after extracapsular cataract extraction (ECCE) and posterior chamber intraocular lens (IOL) implantation in causing iris modifications and in controlling inflammation. SETTING: Outpatients Department, Ninewells Hospital, Dundee, Scotland. METHODS: The prospective study comprised 136 patients who had standardized ECCE. Half the patients used a mydriatic for 2 weeks postoperatively. Anterior chamber activity, pain, and eye redness were evaluated at 2 weeks postoperatively; pupil shape, peripheral anterior synechias, IOL position, and iris adhesions, at 6 weeks. RESULTS: Iris-lens adhesions were significantly more common in the group using a mydriatic. There was no difference between the two groups in postoperative inflammation. CONCLUSION: Mydriatics should not be used routinely after ECCE with posterior chamber IOL implantation. 相似文献
909.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9 相似文献
910.
Variable rate speech coding is now recognized as an important system component for high-capacity cellular networks because it exploits speech statistics to reduce the average bit rate, which results in reduced interference and increased capacity. Once a variable rate capability is available, an additional capacity enhancement can be achieved by introducing network control of the user bit rate in response to changing traffic levels. We introduce the concept of network control of rate and propose a particular network-control method for code-division multiple access (CDMA) systems. Based on an M/M/∞//M queueing model applied to a cell under heavy traffic conditions and a new performance measure called averaged speech quality, we obtain simulation results to demonstrate how network control of rate can achieve improved speech quality or increased capacity for a given quality objective 相似文献