全文获取类型
收费全文 | 370927篇 |
免费 | 25370篇 |
国内免费 | 12526篇 |
专业分类
电工技术 | 18324篇 |
技术理论 | 56篇 |
综合类 | 20185篇 |
化学工业 | 60163篇 |
金属工艺 | 18981篇 |
机械仪表 | 21997篇 |
建筑科学 | 26232篇 |
矿业工程 | 11216篇 |
能源动力 | 10150篇 |
轻工业 | 20605篇 |
水利工程 | 5794篇 |
石油天然气 | 22773篇 |
武器工业 | 2603篇 |
无线电 | 38104篇 |
一般工业技术 | 42617篇 |
冶金工业 | 39211篇 |
原子能技术 | 3396篇 |
自动化技术 | 46416篇 |
出版年
2024年 | 1021篇 |
2023年 | 5104篇 |
2022年 | 8165篇 |
2021年 | 12305篇 |
2020年 | 9552篇 |
2019年 | 7809篇 |
2018年 | 9390篇 |
2017年 | 10825篇 |
2016年 | 10094篇 |
2015年 | 12871篇 |
2014年 | 16185篇 |
2013年 | 19474篇 |
2012年 | 22266篇 |
2011年 | 24784篇 |
2010年 | 19841篇 |
2009年 | 19056篇 |
2008年 | 18556篇 |
2007年 | 18003篇 |
2006年 | 18825篇 |
2005年 | 19327篇 |
2004年 | 12828篇 |
2003年 | 11107篇 |
2002年 | 8945篇 |
2001年 | 8193篇 |
2000年 | 8278篇 |
1999年 | 10222篇 |
1998年 | 14227篇 |
1997年 | 10497篇 |
1996年 | 8800篇 |
1995年 | 6746篇 |
1994年 | 5395篇 |
1993年 | 4156篇 |
1992年 | 2707篇 |
1991年 | 2238篇 |
1990年 | 1779篇 |
1989年 | 1485篇 |
1988年 | 1280篇 |
1987年 | 855篇 |
1986年 | 706篇 |
1985年 | 489篇 |
1984年 | 294篇 |
1983年 | 270篇 |
1982年 | 318篇 |
1981年 | 298篇 |
1980年 | 315篇 |
1979年 | 126篇 |
1978年 | 130篇 |
1977年 | 646篇 |
1976年 | 1374篇 |
1975年 | 118篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
提出了溅射-气体-聚集共沉积制备金属/金属(介质)复合团簇镶嵌薄膜的新方法,并利用该方法成功地在方华膜衬底上制备了系列Fe/Ag及CaF2复合团簇镶嵌薄膜样品。透射电镜分析结果表明,样品中Fe(Cu)团簇都较好地镶嵌于Ag(CaF2)基质中,其结构为两种材料的多晶共存形态。进一步分析发现,与块材相比,Fe/Ag样品中Fe团簇晶格常数呈现出不同程度的收缩,而Cu/CaF2样品中Cu团簇晶格常数则呈现出不同程度的膨胀。运用附加压力的模型对该现象进行了解释。 相似文献
972.
J Tyson L Tranebjaerg S Bellman C Wren JF Taylor J Bathen B Aslaksen SJ S?rland O Lund S Malcolm M Pembrey S Bhattacharya M Bitner-Glindzicz 《Canadian Metallurgical Quarterly》1997,6(12):2179-2185
The Jervell and Lange-Nielsen syndrome (JLNS) comprises profound congenital sensorineural deafness associated with syncopal episodes. These are caused by ventricular arrhythmias secondary to abnormal repolarisation, manifested by a prolonged QT interval on the electrocardiogram. Recently, in families with JLNS, Neyroud et al. reported homozygosity for a single mutation in KVLQT1 , a gene which has previously been shown to be mutated in families with dominantly inherited isolated long QT syndrome [Neyroud et al . (1997) Nature Genet ., 15, 186-189]. We have analysed a group of families with JLNS and shown that the majority are consistent with mutation at this locus: five families of differing ethnic backgrounds were homozygous by descent for markers close to the KVLQT1 gene and a further three families from the same geographical region were shown to be homozygous for a common haplotype and to have the same homozygous mutation of the KVLQT1 gene. However, analysis of a single small consanguineous family excluded linkage to the KVLQT1 gene, establishing genetic heterogeneity in JLNS. The affected children in this family were homozygous by descent for markers on chromosome 21, in a region containing the gene IsK . This codes for a transmembrane protein known to associate with KVLQT1 to form the slow component of the delayed rectifier potassium channel. Sequencing of the affected boys showed a homozygous mutation, demonstrating that mutation in the IsK gene may be a rare cause of JLNS and that an indistinguishable phenotype can arise from mutations in either of the two interacting molecules. 相似文献
973.
974.
Base excision repair (BER) constitutes a ubiquitous excision repair mechanism, which is responsible for the removal of multiple types of damaged and inappropriate bases in DNA. We have employed a yeast cell-free system to examine the biochemical mechanism of the BER pathway in lower eukaryotes. Using uracil-containing DNA as a model substrate, we demonstrate that yeast BER requires Apn1 protein, an Escherichia coli endonuclease IV homolog. In extracts of an apn1 deletion mutant, the 5'-incision at AP (apurinic/apyrimidinic) sites is not detectable, supporting the notion that yeast contains only one major 5'-AP endonuclease. The processing of the 5'-deoxyribose phosphate moieties was found to be a rate-limiting step. During BER of uracil-containing DNA, repair patch sizes of 1-5 nucleotides were detected, with single nucleotide repair patches predominant. 相似文献
975.
S Mattila L Heikkil? J Sipponen K Verkkala K Ky?sola T Mattila A J?rvinen R Luosto L Heikkinen P Ketonen J Salo A Nemlander I Mattila MS Nieminen 《Canadian Metallurgical Quarterly》1997,86(2):113-120
BACKGROUND: Clearance of large molecules from the interstitial space is an important function of lymphatics and is affected by local pathologic changes. OBJECTIVE: To determine if the clearance rate of interstitially injected albumin is correlated to tumour characteristics and outcome in women with invasive breast cancer. METHOD: In a consecutive series of women coming to biopsy for suspected breast cancer, technetium-tagged albumin was injected into the tissue adjacent to the palpable mass. The isotope disappearance rate was measured over two hours. Also assessed were the maximum vessel density (MVD-using Factor VIII polyclonal antisera), the proliferation rate (using Ki-67 antisera), node status, tumour size, histologic and nuclear grade, mitotic rate, and p53 and c-erbB-2 oncoproteins. All patients were followed until relapse and for a minimum of 10 years. RESULTS: In multivariate analysis, an association between relapse-free survival and isotope clearance rate was suggested (p = 0.024). The best outcome was seen in patients with the least isotope clearance. Node status, size, histologic and nuclear grade, and mitotic rate correlated with survival. MVD did not correlate with survival and was inversely related to the isotope clearance rate. Tumour proliferation rate, and the c-erbB-2 and p53 oncoproteins did not relate to outcome. CONCLUSION: The role of lymphatics in breast cancer is difficult to study. Measurement of interstitial clearance may be a useful technique and could be a prognostic factor. 相似文献
976.
H9000系统在西北电网水调自动化系统工程中的应用 总被引:2,自引:0,他引:2
西北电网水调自动化系统主要用于自动采集管理西北电网分布在三大水系的8个水电厂、相关流域内100个水文站、200个雨量站的实时信息,以便实现水库群跨流域补偿,统一协调发电与防洪、排沙、防凌、灌溉等一系列矛盾,解决水库群综合利用问题.系统主要具有上。下特点:(1)开放的系统环境;(2)高可乘性;(3)多样化的数据规约;(4)开放的人机联系手段;(5)务性能的数据库;(6)丰富的水调应用软件.其中水调应用软件包括:(1)汉江上游石泉、安康梯级联合洪水预报;(2)黄河上游龙羊峡、李家峡、刘家峡两库三站短期(日)调度;(3)水务综合统计分析软件.西北水调自动化系统将使H9000系统在大规模网络关系数据库管理技术、高级图形处理技术、复杂网络组网技术、容措技术、水调高级应用软件技术等方面提高到一个更高的水平. 相似文献
977.
VP Korhonen M Tolvanen JM Hyttinen M Uusi-Oukari R Sinervirta L Alhonen M Jauhiainen OA J?nne J J?nne 《Canadian Metallurgical Quarterly》1997,245(2):482-489
We have generated several transgenic mouse lines and rabbits expressing efficiently (up to 0.3 mg/ml in mice and up to 0.5 mg/ml in rabbits) human erythropoietin in their milk as bovine beta-lactoglobulin fusion protein. Human erythropoietin cDNA was inserted in frame into exon 5 of the bovine beta-lactoglobulin gene with a linker oligonucleotide encoding the cleavage site for bacterial IgA protease. RNA analysis performed on one lactating transgenic mouse and one transgenic rabbit revealed that the fusion gene was expressed almost exlusively in the mammary gland, although low amounts of transgene-derived RNA were detectable in salivary glands and uterus or in the kidney. The fusion protein was specifically cleaved with IgA protease. The erythropoietin part obtained upon digestion had a lower molecular mass than recombinant erythropoietin produced in Chinese hamster ovary cells. By deglycosylation analysis it was shown that the difference in size was due to a different type of glycosylation. Biological activity of the fusion protein, as determined by growth stimulation of TF-1 erythroleukemia cells, was less than 15% of that of human recombinant erythropoietin. Upon digestion of the fusion protein with IgA protease, biological activity comparable to that of the recombinant erythropoietin was recovered. Transgenic males and virgin females did not show signs of enhanced erythropoiesis, but lactating females expressing the transgene displayed transient increases in their hematocrit values. 相似文献
978.
A Nu?ez C De la Roza ML Rodrigo-Angulo W Bu?o F Reinoso-Suárez 《Canadian Metallurgical Quarterly》1997,754(1-2):1-11
This study analyses the relationship between the use of rotating instruments, the production of a smear layer and the presence of alterations to enamel microstructures. The rotating instruments used were carbide (8-12 blade) and diamond tipped (30-15 m) cutters. Cavities were made in extracted teeth. Subsequently, half the sample was analysed using the rugosimeter before and after the application of ortophosphoric acid at 35% for 15 and the other half suing a Scansion Electronic microscope (SEM). The results obtained showed on the one hand that carbide cutters leave a smoother surfacer than diamond tipped cutters, and on the other that the smear layer is eliminated better by carbide cutters compared to diamond tipped cutters. Moreover, there are no major traumatic-type alterations at the level of the enamel affecting the microstructure after the use of carbide cutters. 相似文献
979.
AG Labetskaia KM Kireenko IV Ba?dakova IM Tishechkina 《Canadian Metallurgical Quarterly》1997,31(5):391-396
The study of the micromammalian parasite complexes in the Belorussian part of the evacuation zone of the Chernobyl nuclear station revealed 13 species of Coccidia and 30 species of ectoparasitic Arthropoda. Total increase of abundance and biodiversity of both parasites and their hosts was observed. The part of ectoparasites being epidemically hazardous was significantly increased. An analysis of a long-term dynamics of parasite abundance reveals their adaptation to new conditions in the Belorussia. 相似文献
980.
Previous film autoradiographic studies demonstrated that, during corticogenesis, dopamine receptors of the D1 class are abundant in the embryonic primate cerebral wall. In the present study, we expand these findings by identifying the cellular elements of the fetal occipital cerebral wall expressing D1 and D5 subtypes of the D1 dopamine receptor class. We have examined tissue from monkey fetuses collected at 70, 90 and 120 days of gestation using antibodies directed against C-termini of the D1 and D5 dopamine receptors. At all three embryonic ages studied, we found D1 and D5 receptors expressed by multiple cell types of the embryonic cerebral wall. Both D1 and D5 receptor proteins are produced by pyramidal neurons of the cortical plate and by a variety of interstitial neurons of the subplate and intermediate zones. D1 and D5 receptors are also present in cells of the proliferative ventricular and subventricular zones, some of which were identified as dividing cells. In addition, D1 and D5 receptors are detectable in the protoplasmic astroglial and ependymal cells distinguishable in monkey fetuses collected at 120 days of gestation. Some cellular elements of the embryonic monkey cerebral wall express only one subtype of the D1 dopamine receptor class. For example, embryonic Cajal-Retzius neurons in the marginal zone and migrating neurons in the intermediate zone are immunoreactive only to D5 antisera. In contrast, radial glia can be labeled only with D1 receptor-specific antisera. Finally, only D1 receptors are detectable in the blood vessels penetrating the embryonic monkey cerebral wall. Based on these observations, we propose that dopamine receptors of the D1 class play an important role in regulating cerebral cortical formation and that D1 and D5 receptor subtypes may participate in regulation of different aspects of this process. 相似文献