全文获取类型
收费全文 | 20353篇 |
免费 | 1783篇 |
国内免费 | 955篇 |
专业分类
电工技术 | 1166篇 |
技术理论 | 3篇 |
综合类 | 1322篇 |
化学工业 | 2634篇 |
金属工艺 | 970篇 |
机械仪表 | 1179篇 |
建筑科学 | 1541篇 |
矿业工程 | 464篇 |
能源动力 | 473篇 |
轻工业 | 1174篇 |
水利工程 | 308篇 |
石油天然气 | 843篇 |
武器工业 | 170篇 |
无线电 | 2100篇 |
一般工业技术 | 2017篇 |
冶金工业 | 3867篇 |
原子能技术 | 178篇 |
自动化技术 | 2682篇 |
出版年
2024年 | 90篇 |
2023年 | 326篇 |
2022年 | 577篇 |
2021年 | 873篇 |
2020年 | 642篇 |
2019年 | 490篇 |
2018年 | 506篇 |
2017年 | 543篇 |
2016年 | 532篇 |
2015年 | 743篇 |
2014年 | 890篇 |
2013年 | 967篇 |
2012年 | 1073篇 |
2011年 | 1087篇 |
2010年 | 1009篇 |
2009年 | 916篇 |
2008年 | 996篇 |
2007年 | 911篇 |
2006年 | 883篇 |
2005年 | 828篇 |
2004年 | 671篇 |
2003年 | 511篇 |
2002年 | 524篇 |
2001年 | 450篇 |
2000年 | 435篇 |
1999年 | 507篇 |
1998年 | 1234篇 |
1997年 | 815篇 |
1996年 | 611篇 |
1995年 | 407篇 |
1994年 | 351篇 |
1993年 | 348篇 |
1992年 | 146篇 |
1991年 | 121篇 |
1990年 | 124篇 |
1989年 | 120篇 |
1988年 | 98篇 |
1987年 | 86篇 |
1986年 | 66篇 |
1985年 | 46篇 |
1984年 | 16篇 |
1983年 | 25篇 |
1982年 | 31篇 |
1981年 | 27篇 |
1980年 | 58篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1977年 | 106篇 |
1976年 | 218篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
51.
HJ Voeller M Augustus V Madike GS Bova KC Carter EP Gelmann 《Canadian Metallurgical Quarterly》1997,57(20):4455-4459
Loss of heterozygosity at chromosome 8p21-22 is common in human prostate cancer, suggesting the presence of one or more tumor suppressor genes at this locus. A homeobox gene that is expressed specifically in adult human prostate, NKX3.1, the expression of which is regulated by androgen, maps to chromosome 8p21. Fine structure in situ mapping showed that NKX3.1 is proximal to MSR32 (macrophage scavenger receptor type II) and LPL (human lipoprotein lipase) and very close to NEFL (human neurofilament light chain) on 8p21. Single-strand conformational polymorphism analysis of 48 radical prostatectomy cancer specimens and 3 metastases for the entire coding region of NKX3.1 showed no tumor-specific sequence alterations in 50 specimens and total absence of the gene in 1 specimen known to have a biallelic deletion of 8p21. NKX3.1 was found to have a polymorphism at nucleotide 154 in codon 52 that resulted in a CGC-->TGC sequence change and an Arg-->Cys amino acid alteration (R52C). This polymorphism was present in 20% of DNA samples. If NKX3.1 is a target of the 8p21 LOH, it is not via disruption of the coding region of the gene. 相似文献
52.
Cultured hepatocytes of silver eel actively secreted only chylomicron-like lipoprotein. The rate of secretion per mg cellular protein per 24 hr was 2.2 times higher compared with that by yellow eel hepatocytes. Silver eel hepatocytes secreted lipids 2.5 times higher through the lipoprotein than yellow eel hepatocytes. Main lipid was triacylglycerol in either secreted lipoprotein and composition of apolipoproteins of both secreted lipoproteins was the same. The incorporation of 3H-leucine into the lipoprotein secreted by silver eel hepatocytes was 2.4 times higher, but that of 14C-acetate was not significantly different. Protein and lipids composition of plasma lipoproteins of silver eel was significantly higher and lower compared with those of yellow eel, respectively. We suggest that the secreted lipoprotein of silver eel hepatocytes transport much more lipids to other tissues than that of yellow eel hepatocytes. 相似文献
53.
54.
The mode of interaction between muramyl dipeptide (MDP), a compound with immunopharmacological activities, and 5-hydroxtryptamine (5-HT, serotonin) was studied in isolated nerve-smooth muscle preparations of the carp stomach. Application of exogenous 5-HT evoked direct smooth muscle contractions; electric neurogenic stimulation evoked twitches due to release of 5-HT from nerve endings. Contractions evoked by a high concentration of 5-HT (3-30 microM) were resistant to atropine and potentiated in the presence of MDP. Isamoltan (5-HTID antagonist) decreased the amplitude of contractions, whereas ketanserin (5-HT2 antagonist) and MDL 72,222 (5-HT3 antagonist) had no effect. The addition of low concentrations (0.1-1.5 microM) of 5-HT did not contract the preparation but caused a decrease in the amplitude of neurogenic twitches, which might be due to the presynaptic inhibition of serotonin release. This effect of 5-HT was not changed by isamoltan or ketanserin, but it was largely reduced in the presence of 5-HT3 antagonists tropisetron and MDL 72,222. This inhibitory effect of 5-HT on twitch amplitude was potentiated by MDP. The interaction of MDP with the serotonergic system thus involved not only potentiation of the postsynaptic effect of higher 5-HT concentrations, which might have been mediated via the 5-HT1 subsystem, but also presynaptic inhibition. MDP enhancement of 5-HT's inhibitory effect, mediated via 5-HT3 receptors, might represent a new feature in mutual 5-HT-MDP interactions. 相似文献
55.
56.
57.
吸附制冷循环的热力计算及热力学评价方法探讨 总被引:4,自引:0,他引:4
在化工吸附,吸附热力学及Polanyi吸附位势理论的基础上,介绍吸附制冷基本型循环,推演其参数坐标图,进而分析,给出其主要性能指标的热力计算,然后以热力学的逆卡诺循环和内可逆三热源循环模型为指针,对此制冷循环进行考察。并结合热力计算对其热力学完善性做出评价,从而给出了吸附制冷基本型循环合适的热力学评价方法。 相似文献
58.
59.
A method of positive identification of the specificity of polymerase chain reaction (PCR) product using internal oligonucleotide probe is introduced. The hybridization was done on the agarose gel which was dried after electrophoresis. Detection of the expression of T cell receptor a chain variable (TCR V alpha) genes on mRNA level was used as the experimental model. Twenty nine TCR V alpha gene subfamilies could be distinguished clearly in healthy human peripheral blood lymphocytes by this method. Positive identification of PCR product on dried agarose gel by internal oligonucleotide probe is relatively simple and less time consuming. 相似文献
60.
F van Rhee RM Szydlo J Hermans A Devergie F Frassoni W Arcese T de Witte HJ Kolb D Niederwiser N Jacobsen G Gahrton G Bandini E Carreras A Bacigalupo M Michallet T Ruutu J Reiffers JM Goldman J Apperley A Gratwohl 《Canadian Metallurgical Quarterly》1997,20(7):553-560
The purpose of this study was to determine the long-term results of allogeneic bone marrow transplantation for chronic myeloid leukemia. A retrospective analysis was carried out of the outcome of 373 consecutive transplants performed at 38 European institutions between 1980 and 1988 and reported to the registry of the European Group for Blood and Marrow Transplantation. All transplants were carried out for first chronic phase of chronic myelogenous leukemia using unmanipulated marow cells from HLA-identical sibling donors. The probability of survival and leukemia-free survival at 8 years were 54% (95% CI: 49-59) and 47% (95% CI: 41-52) respectively. The probabilities of developing acute GVHD (II-IV) at 100 days and chronic GVHD at 4 years after transplant were 47% (95% CI: 41-53) and 52% (95% CI: 46-58) respectively. The probabilities of transplant-related mortality and leukemic relapse 8 years after BMT were 41% (95% CI: 36-48) and 19% (95% CI: 14-25), respectively. Transplant within 12 months of diagnosis was associated with reduced transplant-related mortality (34 vs 45%, P = 0.013) and resulted in improved leukemia-free survival (52 vs 44%, P = 0.03). The probability of relapse was significantly reduced in patients who developed chronic GVHD (RR = 0.33, P = 0.004). The probability of relapse occurring more than 2 years after transplant was increased more than five-fold in patients transplanted from a male donor (RR = 5.5, P = 0.006). Sixty-seven patients in hematologic remission were studied for residual disease by two-step RT/PCR for BCR-ABL mRNA and 61 (91%) tested negative. We conclude that bone marrow transplantation can induce long-term survival in approximately one-half of CML patients; the majority of survivors have no evidence of residual leukemia cells when studied by molecular techniques. The probability of late relapse is increased with use of a male donor. 相似文献