全文获取类型
收费全文 | 22269篇 |
免费 | 1992篇 |
国内免费 | 932篇 |
专业分类
电工技术 | 1201篇 |
综合类 | 1030篇 |
化学工业 | 3743篇 |
金属工艺 | 1463篇 |
机械仪表 | 1643篇 |
建筑科学 | 1269篇 |
矿业工程 | 608篇 |
能源动力 | 816篇 |
轻工业 | 1523篇 |
水利工程 | 313篇 |
石油天然气 | 970篇 |
武器工业 | 115篇 |
无线电 | 2972篇 |
一般工业技术 | 3589篇 |
冶金工业 | 1249篇 |
原子能技术 | 184篇 |
自动化技术 | 2505篇 |
出版年
2024年 | 108篇 |
2023年 | 462篇 |
2022年 | 776篇 |
2021年 | 1110篇 |
2020年 | 826篇 |
2019年 | 677篇 |
2018年 | 820篇 |
2017年 | 776篇 |
2016年 | 802篇 |
2015年 | 914篇 |
2014年 | 1110篇 |
2013年 | 1348篇 |
2012年 | 1446篇 |
2011年 | 1609篇 |
2010年 | 1380篇 |
2009年 | 1354篇 |
2008年 | 1224篇 |
2007年 | 1016篇 |
2006年 | 976篇 |
2005年 | 851篇 |
2004年 | 652篇 |
2003年 | 635篇 |
2002年 | 590篇 |
2001年 | 498篇 |
2000年 | 465篇 |
1999年 | 472篇 |
1998年 | 455篇 |
1997年 | 353篇 |
1996年 | 326篇 |
1995年 | 260篇 |
1994年 | 209篇 |
1993年 | 137篇 |
1992年 | 111篇 |
1991年 | 77篇 |
1990年 | 74篇 |
1989年 | 63篇 |
1988年 | 43篇 |
1987年 | 34篇 |
1986年 | 33篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Sae-Kyoung Kang Tae-Woo Lee D.V. Plant Hyo-Hoon Park 《Photonics Technology Letters, IEEE》2006,18(1):70-72
A novel bidirectional complementary metal-oxide-semiconductor (CMOS) transceiver for chip-to-chip optical interconnects operating at 2.5 Gb/s is proposed, which shares the common block of a receiver and a transmitter on a single chip. The share of the common block of two circuits makes it possible to save 55% or 20% of power dissipation, depending on the operating mode. The chip in 0.18-/spl mu/m CMOS technology occupies an area of 0.82/spl times/0.82 mm/sup 2/, 70% of the total area of a typical unshared transceiver chip. The transmitting and receiving modes of operation show -3-dB bandwidths of 2.2 and 2.4 GHz and electrical isolations of -28 and -40 dB, respectively. 相似文献
72.
73.
“对于建筑事业,没有什么比让全民的建筑意识提高更重要的事情了。”五十多年前,年轻的齐康对此深信不疑,如今已是古稀之年的齐老对此仍然耿耿于怀。对于青年一代的教育,他从未放松;传统与现代的比较、东方与西方差异的研究,他从未停止。从本期起,我们将连续刊登齐康系列文章《建筑课》。 相似文献
74.
设计师做自己办公空间设计往往想法很多,也很苛求。这种设计状态会令将来的作品显得杂乱、稚嫩, 容易出现“昏招”,或者流于刻板、拘谨、不灵动。我懂得调整自己的状态:有时记住自己是甲方,可以任意发挥,有时把它忘了,也就不必太苛求,以致经常改动设计,不坚决。由于急于搬迁的缘故,加之那时我正好出差在外,所以本案设计周期较短。几天时间在宾馆里伏案设计,倒给出了一个好的状态:略去许多泉涌的想法, 只抓住最好的,好比画者在做速写,把控大局。凭我个人的喜好和习惯,以及对设计公司办公空间的理解与思考,我在凝神中拔高自己,发现塑造一种力量空间会比较接近于表达设计师这种群体的周遭环境,无需过多地出招,无需捕捉人的眼球。力量是潜在的,它无处不在,闭着眼也能抓住你的心。我就这样确立了设计主旨。 相似文献
75.
Yong-Seo Park Seong-Gook Kang Alma Leticia Martinez Ayala Olga Martín-Belloso Shela Gorinstein 《LWT》2006,39(7):748-755
Fresh persimmons were subjected to two different processes: sun-drying during 1 month and dehydration at 60 °C during 12 h. To assess the effect of this process on nutritional and health-related properties of persimmons dietary fibers, minerals, trace elements, polyphenols and the total radical scavenging activities (TRSAs) were determined before and after processing. It was found that the contents of dietary fibers, minerals and trace elements in fresh and dried persimmons fruits were comparable. Total polyphenols in fresh persimmons was higher than in dried fruits (1.3 vs. 0.9 and 0.8 mg/100 g FW, respectively) and percentage of inhibition was higher than in dried fruits (70% vs. 59% and 55% and 58% vs. 53% and 46% for 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) [ABTS] radicals, respectively (P>0.05 in all cases). In conclusion: (1) the differences in the contents of dietary fibers, minerals and trace elements in fresh and dried persimmons are not significant; (2) the contents of polyphenols and the level of the TRSA are higher in fresh persimmons than in dried fruits; however, both variables are also high in dried persimmons; (3) when fresh fruits are not available, proper dried persimmons could be used as a valuable substitute. 相似文献
76.
JK Kang SW Lee MW Baik BC Son YK Hong CK Jung KH Ryu 《Canadian Metallurgical Quarterly》1998,14(7):297-301
Accurate assessment and replacement of blood loss and fluid-electrolyte deficit during craniosynostosis repair is difficult owing to patient size and the diversity of surgical technique. Forty-three patients undergoing primary craniosynostosis repair over a 10-year period were studied retrospectively to determine blood loss and fluid deficit and to assess blood transfusion practices during both intraoperative and postoperative periods. Blood loss was calculated on the basis of estimated red cell mass (ERCM) and fluid-electrolyte imbalance was investigated with blood samplings. Blood transfusion was considered appropriate if the postoperative or posttransfusion ERCM was within 12% of the preoperative value. Estimated fluid requirement (EFR) was used in 4 ml kg(-1) h(-1) except for neonates. Intraoperatively, 80% of all patients were appropriately managed with respect to blood transfusion and EFR. Postoperatively only 20% of the patients receiving transfusions were transfused appropriately. In 23.3% of these patients (10/43) unexpected respiratory distress developed immediately after their recovery from the anesthesia. With the measurement of estimated blood volume and allowable blood loss, appropriate transfusion could be achieved for the successful treatment of the primary craniosynostosis. 相似文献
77.
本文介绍了一种实用的液态合金离子源结构,我们利用本结构研制成功了Au-Si和Au-Si-Be液态合金离子源,测出了它们的发射特性。 相似文献
78.
SZ Zhou S Cooper LY Kang L Ruggieri S Heimfeld A Srivastava HE Broxmeyer 《Canadian Metallurgical Quarterly》1994,179(6):1867-1875
Recombinant adeno-associated virus 2 (AAV) virions were constructed containing a gene for resistance to neomycin (neoR), under the control of either the herpesvirus thymidine kinase (TK) gene promoter (vTK-Neo), or the human parvovirus B19 p6 promoter (vB19-Neo), as well as those containing an upstream erythroid cell-specific enhancer (HS-2) from the locus control region of the human beta-globin gene cluster (vHS2-TK-Neo; vHS2-B19-Neo). These recombinant virions were used to infect either low density or highly enriched populations of CD34+ cells isolated from human umbilical cord blood. In clonogenic assays initiated with cells infected with the different recombinant AAV-Neo virions, equivalent high frequency transduction of the neoR gene into slow-cycling multipotential, erythroid, and granulocyte/macrophage (GM) progenitor cells, including those with high proliferative potential, was obtained without prestimulation with growth factors, indicating that these immature and mature hematopoietic progenitor cells were susceptible to infection by the recombinant AAV virions. Successful transduction did not require and was not enhanced by prestimulation of these cell populations with cytokines. The functional activity of the transduced neo gene was evident by the development of resistance to the drug G418, a neomycin analogue. Individual high and low proliferative colony-forming unit (CFU)-GM, burst-forming unit-erythroid, and CFU-granulocyte erythroid macrophage megakaryocyte colonies from mock-infected, or the recombinant virus-infected cultures were subjected to polymerase chain reaction analysis using a neo-specific synthetic oligonucleotide primer pair. A 276-bp DNA fragment that hybridized with a neo-specific DNA probe on Southern blots was only detected in those colonies cloned from the recombinant virus-infected cells, indicating stable integration of the transduced neo gene. These studies suggest that parvovirus-based vectors may prove to be a useful alternative to the more commonly used retroviral vectors for high efficiency gene transfer into slow or noncycling primitive hematopoietic progenitor cells, without the need for growth factor stimulation, which could potentially lead to differentiation of these cells before transplantation. 相似文献
79.
植被散射实验数据的特性分析 总被引:1,自引:0,他引:1
本文根据电波所获取的各种樾 射实测数据,分析了它们对不同极化波的响应特性。 相似文献
80.
PURPOSE: To determine the apical versus basolateral polarity of the putative anion exchanger in cultured bovine corneal endothelial cells (BCECs) and to examine the influence of Cl--dependent membrane potential (Em) changes on HCO3- transport. METHODS: BCECs grown on permeable supports were used for independent perfusion of apical and basolateral surfaces. Intracellular pH (pHi) was measured using the fluorescent dye BCECF. Relative changes in Em were measured using the fluorescent dye bis-oxonol. Western blot analysis was used to detect immunoreactivity against the anion exchanger (AE1 or AE2). RESULTS: Cl- removal from apical and basolateral surfaces produced cellular alkalinization (apical side, 0.07 pH units; basolateral side, 0.06 pH units; both sides, 0.20 pH units). Application of 100 microM H2-4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid (DIDS), an anion exchange inhibitor, on the apical side produced an alkalinization (0.02 pH units) followed by acidification (-0.05 pH units), whereas basolateral H2DIDS caused a substantial acidification (-0.16 pH units). In the absence of Na+, Cl- removal from the apical side caused a transient alkalinization (0.03 pH units) followed by a return to baseline; Cl- removal from the basolateral side caused a small (-0.03) acidification. In Na+-free Ringer, apical H2DIDS produced a transient alkalinization (0.02 pH units), whereas basolateral exposure had no effect. 5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), N-phenylanthranilic acid (DPC), and niflumic acid (50-200 microM), known Cl- channel blockers, produced cellular acidification in control Ringer. Niflumic acid hyperpolarized Em and inhibited depolarization after Cl- removal. Western blot analysis failed to detect AE2 expression in cultured BCECs. However, fresh BCECs produced a trace response. CONCLUSIONS: Physiological activity of an apical anion exchanger is weak in cultured BCECs. Cultured BCECs have significant Cl- conductance. Thus, cellular alkalinization after Cl- removal is caused primarily by depolarization of Em, which drives HCO3- influx through the basolateral electrogenic Na+:nHCO3- cotransporter. In contrast with cultured BCECs, AE2 may be present in fresh cells. 相似文献