全文获取类型
收费全文 | 785篇 |
免费 | 10篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 10篇 |
金属工艺 | 6篇 |
机械仪表 | 3篇 |
建筑科学 | 5篇 |
矿业工程 | 1篇 |
能源动力 | 4篇 |
轻工业 | 21篇 |
水利工程 | 1篇 |
无线电 | 14篇 |
一般工业技术 | 22篇 |
冶金工业 | 664篇 |
原子能技术 | 21篇 |
自动化技术 | 22篇 |
出版年
2020年 | 2篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 6篇 |
2011年 | 9篇 |
2010年 | 5篇 |
2009年 | 7篇 |
2008年 | 8篇 |
2007年 | 11篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 23篇 |
1998年 | 177篇 |
1997年 | 117篇 |
1996年 | 76篇 |
1995年 | 42篇 |
1994年 | 36篇 |
1993年 | 37篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 39篇 |
1976年 | 54篇 |
1975年 | 8篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1956年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有795条查询结果,搜索用时 69 毫秒
21.
22.
Simon Woodruff Jennifer K. Baerny Nathan Mattor Don Stoulil Ronald Miller Theodore Marston 《Journal of Fusion Energy》2012,31(4):305-316
The benefits of an energy source whose reactants are plentiful and whose products are benign is hard to measure, but at no time in history has this energy source been more needed. Nuclear fusion continues to promise to be this energy source. However, the path to market for fusion systems is still regularly a matter for long-term (20?+?year) plans. This white paper is intended to stimulate discussion of faster commercialization paths, distilling guidance from investors, utilities, and the wider energy research community (including from ARPA-E). There is great interest in a small modular fusion system that can be developed quickly and inexpensively. A simple model shows how compact modular fusion can produce a low cost development path by optimizing traditional systems that burn deuterium and tritium, operating not only at high magnetic field strength, but also by omitting some components that allow for the core to become more compact and easier to maintain. The dominant hurdles to the development of low cost, practical fusion systems are discussed, primarily in terms of the constraints placed on the cost of development stages in the private sector. The main finding presented here is that the bridge from DOE Office of Science to the energy market can come at the Proof of Principle development stage, providing the concept is sufficiently compact and inexpensive that its development allows for a normal technology commercialization path. 相似文献
23.
T Cartmell T Southgate GS Rees MG Castro PR Lowenstein GN Luheshi 《Canadian Metallurgical Quarterly》1999,19(4):1517-1523
Adenovirus-mediated gene transfer into the brain is associated with significant inflammation and activation of anti-vector and anti-transgene immune responses that curtail the gene delivery of adenoviruses and therapeutic efficacy. Elucidating the molecular mediators of inflammatory and immune responses to adenoviruses injected into the brain should allow us to inhibit their inflammatory actions, thereby reducing vector clearance and enhance adenoviral-mediated gene transfer into the CNS. Cytokines are primary mediators of the immune response and are released during inflammation. Here we report for the first time that injection of replication-deficient adenovirus vectors into the cerebral ventricles of rats causes a rapid increase in body temperature. This fever response precedes any vector-encoded transgene expression and occurs with vectors encoding no transgene, as well as with vectors encoding a therapeutic transgene i.e., HSV1-thymidine kinase. No fever is detected after infection of the striatum, an important brain target in studies on neurodegeneration. After infection of the brain ventricles, CSF levels of immunoreactive tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta increase significantly (up to 300-fold). In the hypothalamus, the locus of thermoregulation in the brain, only IL-1beta and IL-6 are significantly elevated. A neutralizing TNF-alpha antibody has no effect on adenovirus-induced fever. However, pretreatment with either the IL-1 receptor antagonist or the cyclooxygenase inhibitor flurbiprofen completely abolishes adenovirus-induced fever, suggesting that IL-1 and prostaglandins are direct mediators of this response. These results are the first to demonstrate that IL-1, but not TNF-alpha, is the main mediator of a very early inflammatory response to adenovirus in the brain. 相似文献
24.
Northrop Robert B. Woodruff Eileen A. 《IEEE transactions on bio-medical engineering》1986,(11):1010-1020
This paper describes the designs for two novel, nonlinear, discrete, drug injection controllers. The basis for these controllers is integral pulse frequency modulation (IPFM). An IPFM controller injects small boluses of a drug into a pharmacokinetic (PK) plant to achieve regulation of the plant output. Bolus injections are advantageous because they provide a precise knowledge of the times and the cumulative amount of drug injected, and they require a discrete-action pump suitable for digital control, miniaturization, and implantation. 相似文献
25.
GN Nettest 《数据通信》2001,(1):45-49
(GN Nettest) 一、GPRS简介 通用分组无线服务 ( GPRS)系统扩展了当前世界上最流行的第二代移动系统一基于语音的 GSM的应用 ,使其能够收发基于分组的数据 ;同时保留了无线接口的基本内容 ,如时分多路复用和频率分配方案 ,以使 GPRS和 GSM能够共存于同一网络上。 1 .特性 传统的 GSM拨号数据接入为用户提供了最大960 0波特的速率。GPRS能够结合多个 GSM时隙 ,在上行链路和下行链路上 ,最多可以使用八个 GSM时隙 ,提供最高 1 70 kbit/sec的带宽。此外 ,GPRS采用全新的 IP网络“一直在线”接入模式 :移动用户开… 相似文献
26.
J Goswami AJ Sinskey H Steller GN Stephanopoulos DI Wang 《Canadian Metallurgical Quarterly》1999,62(6):632-640
One of the main problems in the culture of Chinese Hamster Ovary (CHO) cells continues to be the inability to maintain the viability of the cultures over an extended period of time. The rapid decline in viability at the end of the culture is exacerbated by the absence of serum. In trying to reduce the extent of death in these cultures, we first tried to determine the mode of death. We found that more than 80% of the cells in a standard serum-free batch culture of CHO cells in suspension died via apoptosis--as evidenced by condensed chromatin and the appearance of a characteristic DNA ladder. Furthermore, when protein synthesis was inhibited using cycloheximide, the cells underwent rapid apoptosis indicating that death proteins were present in greater abundance than survival proteins in our CHO cells. Cell lysate from CHO cells showed evidence of cysteine protease (caspase) activity. Caspases of the Interleukin-1-beta-Converting Enzyme (ICE) family, e.g., CPP32, Mch-1, etc., have been implicated in the apoptotic process. Surprisingly, a caspase peptide inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoro-methyl-ketone (z-VAD.fmk), was unable to substantially extend the life of a serum-free batch culture of CHO cells. In addition, z-VAD.fmk was only marginally able to extend viability in response to withdrawal of growth and survival factors, insulin and transferrin. In both these instances, z-VAD.fmk was able to prevent cleavage of caspase substrates, but not protect cells from death. However, we found that bcl-2 expression was able to significantly extend viabilities in CHO batch culture. Bcl-2 expression also substantially extended the viability of cultures in response to insulin and transferrin withdrawal. These results provide interesting insights into the pathways of death in a CHO cell. 相似文献
27.
A 14 year old girl with double outlet right ventricle, left isomerism, and complicated atrial anatomy had undergone corrective surgery with intra-atrial rerouting at 5 years of age. Cardiac catheterisation eight years after the surgery showed that she had two systemic venous baffle stenoses: between the hepatic vein and caval vein, and the caval vein and right atrium. Two Palmaz stents were successfully implanted percutaneously through a long sheath and a balloon catheter. The stenoses were relieved immediately and her symptoms quickly disappeared. 相似文献
28.
MP Czubryt JC Russell J Sarantopoulos JS Gilchrist GN Pierce 《Canadian Metallurgical Quarterly》1997,176(1-2):327-335
The putative role of the nuclear nucleoside triphosphatase (NTPase) is to provide energy to the nuclear pore complex for poly A(+) mRNA export. Previous work has demonstrated that liver nuclear NTPase activity is greater in 6 month old corpulent (cp/cp) female JCR:LA rats, a hyperlipidemic rat model, compared to lean (+/?) animals. This increase appeared to be related to increases in nuclear membrane cholesterol content. The current study extended these initial data to compare NTPase activity as a function of age and sex in isolated JCR:LA-cp rat liver nuclei, to further test the hypothesis that nuclear membrane cholesterol may modulate NTPase activity. NTPase activity was increased in cp/cp female animals compared to +/? females at all ages studied, with Vmax values increased by 60-176%. Membrane integrity of cp/cp female nuclei was reduced compared to +/? female nuclei. Nuclear membrane cholesterol levels increased linearly with age by 50, 150 and 250% in 3, 6 and 9 month old cp/cp females over leans. In contrast, nuclei from cp/cp males exhibited only minor, isolated changes in NTPase activity. Furthermore, there were no significant changes in nuclear cholesterol content or membrane integrity in the less hyperlipidemic male animals at any age. These data suggest that altered lipid metabolism may lead to changes in nuclear membrane structure, which in turn may alter NTPase activity and functioning of the nuclear pore complex. 相似文献
29.
Assembly of functional cytochrome oxidase in yeast requires Cox17, which has been postulated to deliver copper ions to the mitochondrion for insertion into the enzyme. This role for Cox17 is supported by the observation that it binds copper as a binuclear cuprous-thiolate cluster. X-ray absorption spectroscopy, together with UV-visible absorption and emission spectroscopy, indicates the presence of bound cuprous ions, trigonally coordinated by thiolate ligands. Analysis of the EXAFS shows three Cu-S bonds at 2.26 A, plus a short Cu-Cu distance of 2.7 A, indicating a binuclear cluster in Cox17. The cuprous-thiolate cluster in Cox17 is substantially more labile than structurally related clusters in metallothioneins. 相似文献
30.
Histopathologic studies have demonstrated microshards from silicone elastomer metatarsophalangeal joint implants in adjacent tissues in a setting of chronic inflammation and in inguinal lymph nodes. Cytologic smears of synovial fluid from symptomatic implanted joints should show these refractile, nonpolarizing microshards in the reactive inflammatory context. Nonspecific enzymatic inflammatory activity contributes to further destabilization of the implants, eventuating in symptoms and signs requiring prosthesis removal. Cytopathologic examination of aspirated fluid from the vicinity of a symptomatic implanted joint demonstrates foreign body reaction to silicone elastomer, predicting a need for intervention before the local damage is severe and disabling. 相似文献