全文获取类型
收费全文 | 1298篇 |
免费 | 20篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 8篇 |
综合类 | 1篇 |
化学工业 | 146篇 |
金属工艺 | 30篇 |
机械仪表 | 19篇 |
建筑科学 | 9篇 |
能源动力 | 16篇 |
轻工业 | 32篇 |
石油天然气 | 1篇 |
无线电 | 68篇 |
一般工业技术 | 171篇 |
冶金工业 | 745篇 |
原子能技术 | 3篇 |
自动化技术 | 70篇 |
出版年
2022年 | 4篇 |
2021年 | 17篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 18篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 35篇 |
2012年 | 21篇 |
2011年 | 25篇 |
2010年 | 20篇 |
2009年 | 22篇 |
2008年 | 17篇 |
2007年 | 24篇 |
2006年 | 22篇 |
2005年 | 22篇 |
2004年 | 17篇 |
2003年 | 22篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 37篇 |
1998年 | 204篇 |
1997年 | 133篇 |
1996年 | 96篇 |
1995年 | 51篇 |
1994年 | 51篇 |
1993年 | 49篇 |
1992年 | 17篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 23篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1978年 | 5篇 |
1977年 | 44篇 |
1976年 | 57篇 |
1975年 | 7篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1970年 | 5篇 |
排序方式: 共有1319条查询结果,搜索用时 515 毫秒
91.
This study investigates whether nanoporous micromachined biocapsules, with uniform membrane pore sizes of 24.5-nm, can be used to encapsulate insulin-secreting cells in vitro. This approach to cell encapsulation is based on microfabrication technology whereby immunoisolation membranes are bulk and surface micromachined to present uniform and well-controlled pore sizes as small as 10 nm, tailored surface chemistries, and precise microarchitectures. This study evaluates the behavior of insulinoma cells with micromachined membranes, the effect of matrix configurations within the biocapsule on cell behavior, as well as insulin and glucose transport through the biocapsule membranes. 相似文献
92.
Emily L. Seet Jennifer K. Yee Juanita K. Jellyman Guang Han Michael G. Ross Mina Desai 《Lipids》2015,50(6):565-573
In offspring exposed in utero to a maternal diet high in fat (HF), we have previously demonstrated that despite similar birth weights, HF adult offspring at 6 months of age had significantly higher body weights, greater adiposity, and increased triacylglycerol (TAG) levels as compared to controls. We hypothesized that a maternal HF diet predisposes to offspring adiposity via a programmed increase in the synthesis of monounsaturated fatty acids in the liver and hence increased substrate availability for liver TAG synthesis. We further hypothesized that programmed changes in offspring liver fatty acid metabolism are associated with increased liver expression of the lipogenic enzyme stearoyl‐CoA desaturase‐1 (SCD‐1). Female rats were maintained on a HF diet rich in monounsaturated fatty acids (MUFA) prior to and throughout pregnancy and lactation. After birth, newborns were nursed by the same dam, and all offspring were weaned to control diet. Plasma and liver fatty acid compositions were determined using gas chromatography/mass spectrometry. Fatty acid C16 desaturation indices of palmitoleic/palmitic and (vaccenic + palmitoleic)/palmitic and the C18 desaturation index of oleic/stearic were calculated. Liver protein abundance of SCD‐1 was analyzed in newborns and adult offspring. Plasma and liver C16 desaturation indices were decreased in HF newborns, but increased in the adult offspring. Liver SCD‐1 expression was increased in the HF adult offspring. These data show that the maternal HF diet during pregnancy and lactation increases offspring liver SCD‐1 protein abundance and alters the liver C16 desaturase pathway. 相似文献
93.
Continuous treatment of polyester/cotton blended fabric samples was carried with hexamethyldisiloxane (HMDSO) plasma on the pilot scale atmospheric pressure plasma reactor. The mixture of helium and argon was used as carrier gas for generating dielectric barrier discharge plasma. The effect of discharge power and treatment time on the water repellent properties of samples were evaluated with contact angle (CA) and spray test measurements. Spray test and CA results showed improved resistance to wetting with water. The effect of discharge conditions on the surface morphology and surface chemistry of plasma treated samples were investigated by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopic analysis, respectively. The presence of Si‐O‐Si and Si‐CH3 groups in the structure of plasma polymer deposited at the surface of P/C samples was revealed by FTIR spectroscopy. Further, structural differences in HMDSO plasma polymer deposited under different discharge conditions were reported with reference to organic/inorganic nature of plasma polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011. 相似文献
94.
Brijesh Jajal Vipul Desai 《International journal of imaging systems and technology》2010,20(4):367-369
In recent technocrat world, an alteration of a digital image is more ubiquitous amongst techno‐savvy professionals, which has also been proved recurrent even for laymen. This has been popularized on account of a lucid access of different types of image‐editing software. Copying a particular region from a digital image to selective location within the same image is one of the good citations of image doctoring. Usually, the bitmap pictures are represented in the form of three‐channel color image, in which the algorithm identifies the similar areas with an assumption of image acquisition in 24 bits Bitmap format. In the present article, an exclusive procedure was applied to produce an output image, pinpointing the copy–paste area with more than 90% accuracy. The resultant image was depicting a forgery operation presumed to be performed, which determined two areas of similarity. A novel approach of 1‐connected graph was applied, as the forgery is not believed to be done in the form of a petite point‐like area. Finally, the forgery area was exposed with an aid of discerning color value, commonly as a black color for an apparent visibility of an image. The present application will be a tool in image forensics that can be applicable to identify the copy–paste regions in a single bitmap image. This article refers to a new approach for detecting the image portions which are copied from another image. Besides, the present investigation discusses an algorithm effectively implemented to determine the areas formed by copy–paste operation in an image. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 367–369, 2010 相似文献
95.
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
96.
Arun K. Sharma Jacek Krzeminski Dhimant Desai Shantu Amin 《Polycyclic Aromatic Compounds》2013,33(3):297-305
Syntheses of naphtho[8,1,2- ghi ]chrysene (naphtho[1,2- e ]pyrene, N[ e ]P) 1 , dibenzo[ c,mno ]chrysene (naphtho[1,2- a ]pyrene, N[ a ]P) 2 and their dihydrodiol metabolites are described. The hydrocarbons N[ e ]P 1 and N[ a ]P 2 and their fjord region dihydrodiols 12 and 19 were synthesized using a Suzuki cross-coupling reaction followed by the appropriate manipulation of the functional groups. The K-region cis dihydrodiols of N[ e ]P-4,5-diol 20 , N[ a ]P-4,5-diol 23 , N[ a ]P-7,8-diol 24 were obtained by OsO 4 oxidation. The cis diols thus obtained were first converted to the corresponding quinones with pyridinium chlorochromate and, finally, to the desired trans dihydrodiols 22 , 27 , and 28 by NaBH 4 reduction. The mixture of trans N[ a ]P-4,5- and 7,8-dihydrodiols was separated by high-performance liquid chromatography. 相似文献
97.
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
98.
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
99.
M Chatterjee A Majumder P Iyer G Muthukrishnan MK Das N Ramamoorthy CN Desai S Banerjee 《Canadian Metallurgical Quarterly》1996,23(7):867-872
Technetium-99m-MAG3 is accepted as a renal tubular function agent. However, sporadic liver and gall bladder visualisation during its clinical use is clearly a disadvantage. HPLC-purified 99mTc-MAG3 samples exhibited appreciable hepatobiliary uptake (7%), and an elevated level of such uptake was observed in unpurified kit preparations, which was stated to be associated with the excretory property of the radiolabeled kit impurities. To verify this we attempted to quantitate the hepatobiliary uptake of the kit preparations with that of its radiolabeled components. The contribution of each component toward hepatobiliary uptake of the sample was calculated from their abundance in the chelate mixture and the individual biodistribution of the isolated components. However, the anticipated hepatobiliary uptake of different preparations of 99mTc-MAG3 calculated in this way was always lower than that of the experimental value determined directly. Further work is needed to explain the anomaly. 相似文献
100.
GD Stoner C Adams LA Kresty SG Amin D Desai SS Hecht SE Murphy MA Morse 《Canadian Metallurgical Quarterly》1998,19(12):2139-2143
The ability of dietary isothiocyanates to inhibit the esophageal metabolism of N'-nitrosonornicotine (NNN) was examined in F344 rats. Following feeding of benzyl isothiocyanate (BITC), phenethyl isothiocyanate (PEITC), 3-phenylpropyl isothiocyanate (PPITC), 4-phenylbutyl isothiocyanate (PBITC) or 6-phenylhexyl isothiocyanate for 2 weeks, rats were killed and the esophagi were incubated in vitro with [5-3H]NNN. While dietary BITC, PEITC and PBITC all decreased NNN metabolism, dietary PPITC had the greatest effect, yielding inhibition ranging from 55 to 91% of the control production of various NNN metabolites. To determine the chemopreventive efficacy of PPITC on NNN-induced esophageal tumorigenesis, rats were fed AIN-76A diets containing 0, 1.0 or 2.5 micromol/g PPITC and were given untreated drinking water or drinking water containing 5 p.p.m. NNN. After 87 weeks, the experiment was terminated and the esophageal tumors were counted. Rats that were given untreated drinking water developed no tumors. Rats that were given 5 p.p.m. NNN and unadulterated AIN-76A diet had an esophageal tumor incidence of 71% and a multiplicity of 1.57 tumors/animal. The two dietary concentrations of PPITC reduced the incidence and multiplicity of NNN-induced esophageal tumors by >95%. These results demonstrate the remarkable chemopreventive efficacy of PPITC in the NNN-induced esophageal tumor model. 相似文献