全文获取类型
收费全文 | 10475篇 |
免费 | 42篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 14篇 |
综合类 | 5篇 |
化学工业 | 281篇 |
金属工艺 | 33篇 |
机械仪表 | 24篇 |
建筑科学 | 82篇 |
矿业工程 | 14篇 |
能源动力 | 59篇 |
轻工业 | 148篇 |
水利工程 | 17篇 |
石油天然气 | 18篇 |
武器工业 | 4篇 |
无线电 | 261篇 |
一般工业技术 | 284篇 |
冶金工业 | 8952篇 |
原子能技术 | 27篇 |
自动化技术 | 297篇 |
出版年
2022年 | 11篇 |
2021年 | 18篇 |
2019年 | 14篇 |
2018年 | 24篇 |
2017年 | 15篇 |
2016年 | 27篇 |
2015年 | 21篇 |
2014年 | 30篇 |
2013年 | 107篇 |
2012年 | 46篇 |
2011年 | 76篇 |
2010年 | 42篇 |
2009年 | 47篇 |
2008年 | 71篇 |
2007年 | 65篇 |
2006年 | 65篇 |
2005年 | 55篇 |
2004年 | 47篇 |
2003年 | 57篇 |
2002年 | 44篇 |
2001年 | 34篇 |
2000年 | 45篇 |
1999年 | 332篇 |
1998年 | 2840篇 |
1997年 | 1588篇 |
1996年 | 1045篇 |
1995年 | 596篇 |
1994年 | 481篇 |
1993年 | 587篇 |
1992年 | 98篇 |
1991年 | 126篇 |
1990年 | 142篇 |
1989年 | 124篇 |
1988年 | 121篇 |
1987年 | 115篇 |
1986年 | 116篇 |
1985年 | 94篇 |
1984年 | 34篇 |
1983年 | 34篇 |
1982年 | 52篇 |
1981年 | 54篇 |
1980年 | 100篇 |
1979年 | 20篇 |
1978年 | 32篇 |
1977年 | 209篇 |
1976年 | 472篇 |
1975年 | 25篇 |
1974年 | 11篇 |
1973年 | 21篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
AIMS: This series analyses the results of conservative surgery for large lower pole breast cancers by lumpectomy associated with a bilateral remodelling mammoplasty, in order to avoid residual deformities. METHODS: This retrospective study concerns 50 patients with a lower pole breast cancer treated between 1986 and 1996 by lumpectomy, mammoplasty and irradiation. The contralateral breast was immediately made symmetrical in all cases. The mean tumour size was 32.5 mm. RESULTS: The mean weight of the lumpectomy specimen was 270 g. Resection margins were tumour-free in 90% of cases. The main complication observed was delayed healing, thus postponing post-operative treatment in 6.5% of cases. The median follow-up was 48 months. The 5-year actuarial ipsilateral local recurrence rate was 7% and 5-year actuarial metastasis-free and overall survival rates were 81 and 97%, respectively. Cosmesis was satisfactory in 85% of patients. We observed better results when radiotherapy was performed after rather than prior to surgery (92 vs. 67%: NS). CONCLUSIONS: Performing a bilateral mammoplasty at the time of initial surgery for large breast cancers situated in the lower quadrants of the breast facilitates larger lumpectomies with good cosmetic results. 相似文献
13.
MZ Kounnas EB Loukinova S Stefansson JA Harmony BH Brewer DK Strickland WS Argraves 《Canadian Metallurgical Quarterly》1995,270(22):13070-13075
Glycoprotein 330 (gp330) is a member of a family of endocytic receptors related to the low density lipoprotein receptor. gp330 has previously been shown to bind a number of ligands in common with its family member, the low density lipoprotein receptor-related protein (LRP). To identify ligands specific for gp330 and relevant to its localization on epithelia such as in the mammary gland, gp330-Sepharose affinity chromatography was performed. As a result, a 70-kDa protein was selected from human milk and identified by protein sequencing to be apolipoprotein J/clusterin (apoJ). Solid-phase binding assays confirmed that gp330 bound to apoJ with high affinity (Kd = 14.2 nM). Similarly, gp330 bound to apoJ transferred to nitrocellulose after SDS-polyacrylamide gel electrophoresis. LRP, however, showed no binding to apoJ in either type of assay. The binding of gp330 to apoJ could be competitively inhibited with excess apoJ as well as with the gp330 ligands apolipoprotein E, lipoprotein lipase, and the receptor-associated protein, a 39-kDa protein that acts to antagonize binding of all known ligands for gp330 and LRP. Several cultured cell lines that express gp330 and ones that do not express the receptor were examined for their ability to bind and internalize 125I-apoJ. Only cells that expressed gp330 endocytosed and degraded radiolabeled apoJ. Furthermore, F9 cells treated with retinoic acid and dibutyryl cyclic AMP to increase expression levels of gp330 displayed an increased capacity to internalize and degrade apoJ. Cellular internalization and degradation of radiolabeled apoJ could be inhibited with unlabeled apoJ, receptor-associated protein, and gp330 antibodies. The results indicate that gp330 but not LRP can bind to apoJ in vitro and that gp330 expressed by cells can mediate apoJ endocytosis leading to lysosomal degradation. 相似文献
14.
15.
16.
17.
Human immunodeficiency virus (HIV) infection of the thymus could have profound effects on development of the immune response, particularly in children. We and others have established that in addition to infecting and depleting CD4-bearing thymocytes, functional HIV proviruses are found in thymocytes lacking surface CD4 expression. Using in vitro thymocyte cultures, we show that neither HIV-mediated down regulation of CD4 nor CD4-independent infection contributes to the localization of HIV in cells lacking the primary virus receptor. Rather, infection of a CD4-positive precursor cell (CD4 positive/CD8 positive) with subsequent differentiation into a mature CD4-negative phenotype results in productively infected CD4-negative cells. This novel mechanism may contribute to pathogenesis by distributing viral sequences into functional subsets of T cells typically refractory to HIV infection and could account for the presence of viral DNA in CD8-positive lymphocytes recently observed in patients. 相似文献
18.
Here we are presenting the case of a 70-years-old woman who has hepatic cirrhosis anti-HCV and insulin-dependent diabetes mellitus, without relevant epidemiologic ascendants or previous transfusions and HBV, HIV negatives. On admission to our hospital she showed signs of autoimmune hemolytic anaemia (AHA) which was confirmed by positive direct Coombs test and an improvement in blood test after corticoid treatment. Having discarded other possible causes such as drugs infectious diseases or essential mixed cryoglobulinemia (CME), we put forward the possible association between AHA and infection by HCV, where AHA was an extrahepatic immunological manifestation of HCV. This fact has never been brought to light in previous medical literature. 相似文献
19.
DeTienne D.H. Gray G.R. Agrawal G.P. Lenstra D. 《Quantum Electronics, IEEE Journal of》1997,33(5):838-844
Most of the previous treatments of semiconductor lasers subject to optical feedback from a phase-conjugate mirror (PCM) have assumed that the PCM responds instantaneously. Furthermore, the mechanism responsible for phase conjugation does not usually enter into the analysis. In this paper, we derive the time-dependent reflectivity of a PCM created through nondegenerate four-wave mixing in a Kerr-type nonlinear medium. The resulting laser dynamics are compared with the case of the ideal PCM, as a function of the external-cavity length, the PCM reflectivity, and the PCM interaction depth. The PCM with a significant interaction depth tends to suppress otherwise chaotic output and produces pulses whose repetition rate is tunable by varying PCM reflectivity. At high feedback levels, it stabilizes the laser output. We use the circle-map formalism to explain our numerical results 相似文献
20.
V Kumar PM Carabateas JA Dority WG Earley JP Mallamo C Subramanyam LD Aimone B Ault DL DeHaven Hudkins MS Miller 《Canadian Metallurgical Quarterly》1995,38(10):1826-1830
Replacement of the pyridinium ring of 6,11-ethanobenzo[b]quinolizinium cations with thiazolium (4a and 4b) and N-methylimidazolium (4c and 4d) resulted in equipotent compounds in the [3H]TCP binding assay. The corresponding N-methyl-1,2,4-triazolium analogs were less potent in this assay. The thiazolium derivative 4b, with a Ki = 2.9 nM, is being evaluated as a possible neuroprotective N-methyl-D-aspartic acid (NMDA) antagonist. 相似文献