全文获取类型
收费全文 | 26184篇 |
免费 | 1093篇 |
国内免费 | 39篇 |
专业分类
电工技术 | 178篇 |
综合类 | 26篇 |
化学工业 | 6352篇 |
金属工艺 | 510篇 |
机械仪表 | 492篇 |
建筑科学 | 885篇 |
矿业工程 | 50篇 |
能源动力 | 1068篇 |
轻工业 | 4914篇 |
水利工程 | 216篇 |
石油天然气 | 136篇 |
武器工业 | 2篇 |
无线电 | 1120篇 |
一般工业技术 | 3584篇 |
冶金工业 | 4045篇 |
原子能技术 | 211篇 |
自动化技术 | 3527篇 |
出版年
2024年 | 59篇 |
2023年 | 223篇 |
2022年 | 677篇 |
2021年 | 875篇 |
2020年 | 553篇 |
2019年 | 638篇 |
2018年 | 804篇 |
2017年 | 794篇 |
2016年 | 862篇 |
2015年 | 705篇 |
2014年 | 984篇 |
2013年 | 1860篇 |
2012年 | 1427篇 |
2011年 | 1787篇 |
2010年 | 1378篇 |
2009年 | 1380篇 |
2008年 | 1181篇 |
2007年 | 1055篇 |
2006年 | 835篇 |
2005年 | 711篇 |
2004年 | 664篇 |
2003年 | 600篇 |
2002年 | 537篇 |
2001年 | 376篇 |
2000年 | 368篇 |
1999年 | 403篇 |
1998年 | 1425篇 |
1997年 | 912篇 |
1996年 | 669篇 |
1995年 | 368篇 |
1994年 | 323篇 |
1993年 | 319篇 |
1992年 | 122篇 |
1991年 | 115篇 |
1990年 | 84篇 |
1989年 | 111篇 |
1988年 | 89篇 |
1987年 | 83篇 |
1986年 | 65篇 |
1985年 | 100篇 |
1984年 | 64篇 |
1983年 | 50篇 |
1982年 | 53篇 |
1981年 | 54篇 |
1980年 | 58篇 |
1979年 | 32篇 |
1977年 | 94篇 |
1976年 | 185篇 |
1975年 | 29篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Juan Peragón Eva E. Rufino-Palomares Irene Mu?oz-Espada Fernando J. Reyes-Zurita José A. Lupiá?ez 《International journal of molecular sciences》2015,16(9):21681-21694
Maslinic acid (MA) and oleanolic acid (OA), the main triterpenic acids present in olive, have important properties for health and disease prevention. MA selectively inhibits cell proliferation of the HT29 human colon-cancer cell line by inducing selective apoptosis. For measuring the MA and OA concentration inside the cell and in the culture medium, a new HPLC-MS procedure has been developed. With this method, a determination of the amount of MA and OA incorporated into HT29 and HepG2 human cancer-cell lines incubated with different concentrations of MA corresponding to 50% growth inhibitory concentration (IC50), IC50/2, IC50/4, and IC50/8 has been made. The results demonstrate that this method is appropriate for determining the MA and OA concentration in different types of cultured cells and reveals the specific dynamics of entry of MA into HT29 and HepG2 cells. 相似文献
992.
Tibor Károly Fábián Anita Beck Pál Fejérdy Péter Hermann Gábor Fábián 《International journal of molecular sciences》2015,16(3):5945-5974
The gustatory system plays a critical role in determining food preferences and food intake, in addition to nutritive, energy and electrolyte balance. Fine tuning of the gustatory system is also crucial in this respect. The exact mechanisms that fine tune taste sensitivity are as of yet poorly defined, but it is clear that various effects of saliva on taste recognition are also involved. Specifically those metabolic polypeptides present in the saliva that were classically considered to be gut and appetite hormones (i.e., leptin, ghrelin, insulin, neuropeptide Y, peptide YY) were considered to play a pivotal role. Besides these, data clearly indicate the major role of several other salivary proteins, such as salivary carbonic anhydrase (gustin), proline-rich proteins, cystatins, alpha-amylases, histatins, salivary albumin and mucins. Other proteins like glucagon-like peptide-1, salivary immunoglobulin-A, zinc-α-2-glycoprotein, salivary lactoperoxidase, salivary prolactin-inducible protein and salivary molecular chaperone HSP70/HSPAs were also expected to play an important role. Furthermore, factors including salivary flow rate, buffer capacity and ionic composition of saliva should also be considered. In this paper, the current state of research related to the above and the overall emerging field of taste-related salivary research alongside basic principles of taste perception is reviewed. 相似文献
993.
Eduardo Méndez Julio Sanhueza Hernán Speisky Alfonso Valenzuela 《Journal of the American Oil Chemists' Society》1997,74(3):331-332
Two Rancimat evaluation modes, the induction period (IP), and the time needed to achieve a selected difference in conductivity
(tΔK) were compared for assessing relative stability of anchovy, sardine, and hake liver oils. Mean coefficients of variation
were 2.5 and 2.4% for IP and tΔK values, respectively, for oils oxidized in the range 55–90°C. Natural logarithms of IP and
tΔK values varied linearly with temperature (P<0.001). A linear relationship (r=0.999) was established between the IP and tΔK values (P<0.001). Relative oxidative stability of fish oils was determined with the same degree of confidence by either IP or tΔK values. 相似文献
994.
Helena Valentová Miroslav Kašpar Věra Hamplová Karel Bouchal Michal Ilavský Antonín Sikora Daniel Froelich René Muller 《Polymer Bulletin》1997,38(2):219-226
The dynamic mechanical behaviour of random copolymers of LC monomer-1-(hexyloxycarbonyl)ethyl 4-[4-(methacryloyloxy)benzoyloxy]benzoate
(HB) and octyl methacrylate (OMA) was studied in the main transition and flow regions. Even though the aliphatic end groups
of the side chain of HB and OMA are roughly the same, the T
g temperature of poly(HB) is ∼ 80 K higher than that of poly(OMA); this fact is due to the presence of the stiff phenyl benzoate
mesogenic group in the side chain of HB. With increasing content of OMA in the copolymer the superimposed curves of the storage
G′
p and loss G′′
p moduli at a constant temperature shift towards shorter frequencies. It has been shown that this shift is mainly due to an
increase of the free volume in the copolymers with increasing content of OMA. While HB monomer shows liquid crystalline (LC)
properties, its polymer (poly(HB)) and random copolymers with OMA show only isotropic thermal behaviour because no flexible
spacer is present in the side chain of HB which would decouple the main chain and mesogenic group motions. This means that
neither the homopolymer of HB, nor its copolymers with a flexible comonomer retain the LC properties of the starting LC monomer,
HB.
Received: 26 September 1996/Revised: 7 November 1996/Accepted: 7 November 1996 相似文献
995.
Jos M. Monteagudo Lourdes Rodríguez Jesusa Rincn Juan Fuertes 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1997,68(3):271-276
The fermentation kinetics for the conversion of beet molasses, a valuable and economical fermentation substrate, to lactic acid by the homofermentative organism Lactobacillus delbrueckii C.E.C.T. 286 have been studied at controlled pH and temperature under anaerobic batch conditions. An inhibitory effect of lactic acid on fermentation of beet molasses has been found. The bacterium was able to produce lactic acid even after growth ceased. A kinetic model for the fermentation is proposed. From this model, the maximum allowable lactic acid concentration above which growth stops and the lactic acid level above which bacteria stop producing lactic acid were found to be 45 g dm−3 and 57 g dm−3, respectively. © 1997 SCI. 相似文献
996.
A. Nilgün Akn Z. lsen
nsan 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1997,70(3):304-310
The kinetics of CO hydrogenation over coprecipitated 36 wt% Co/Al2O3 was studied in a fixed-bed microreactor at atmospheric pressure. Intrinsic kinetic data were obtained in the initial rate region using four different CO concentrations and two different H2/CO ratios over the 473–523 K temperature range. The surface carbide mechanism with dissociative adsorption of hydrogen as the rate controlling step gives the most plausible kinetic model among the eight different models tested. C1–C4 production rates are found to be strongly influenced by temperature, and optimum C1–C4 hydrocarbon selectivity is obtained at 508 K. The activation energy for CO consumption and CH4 formation are calculated as 74±2 kJ mol−1 and 84±2 kJ mol−1 respectively. ©1997 SCI 相似文献
997.
Esra Bozkır Nurşen Sarı Hatice Öğütcü 《Journal of Inorganic and Organometallic Polymers and Materials》2012,22(5):1146-1155
An investigation of antimicrobial properties of 12 novel modified polymer derived from the condensation reaction of (aminomethyl)polystyrene and four substitute salicylaldehyde (2-hydroxy benzaldehyde, 5-fluoro-2 hydroxy benzaldehyde, 5-fluoro-3-chloro-salicylaldehyde and 5-fluoro-3-methyl-salicylaldehyde) has been carried out and Cr(III) and Ni(II) complexes have been prepared. Modified polymers were characterized by magnetic susceptibility, elemental analyses, and spectral studies. The 1H NMR and 13C NMR spectra analysis of the polymeric carbinolamine/azomethine were determined. In addition, surface morphology and composition were determined by SEM/EDX. Thermo gravimetric analyses of polymers were carried out in nitrogen atmosphere. Antibacterial activities of the polymers attached carbinolamine/azomethine and their complexes were studied by the well-diffusion method against Listeria monocytogenes 4b, Staphylococcus aureus, Escherichia coli, Salmonella typhi H, Brucella abortus, Staphylococcus epidermis sp., Micrococcus luteus, Shigella dysenteria type 10, Bacillus cereus, Pseudomonas putida and antifungal activity against Candida albicans. 相似文献
998.
999.
An activated carbon, Carbochem(TM)-PS230, was modified by chemical and thermal treatment in flow of H(2), in order to evaluate the influence of the activated carbon chemical characteristics in the adsorption of the catechol. The catechol adsorption in aqueous solution was studied along with the effect of the pH solution in the adsorption process of modified activated carbons and the variation of immersion enthalpy of activated carbons in the aqueous solutions of catechol. The interaction solid-solution is characterized by adsorption isotherms analysis, at 298 K and pH 7, 9 and 11 in order to evaluate the adsorption value above and below that of the catechol pK(a). The adsorption capacity of carbons increases when the solution pH decreases. The retained amount increases slightly in the reduced carbon to maximum adsorption pH and diminishes in the oxidized carbon. Similar conclusions are obtained from the immersion enthalpies, whose values increase with the solute quantity retained. In granular activated carbon (CAG), the immersion enthalpies obtained are between 21.5 and 45.7 J·g(-1) for catechol aqueous solutions in a range of 20 at 1500 mg·L(-1). 相似文献
1000.
Guadalupe Aparicio Gallego Vanessa Medina Villaamil Enrique Grande Isabel Santamarina Ca��nzos Lu��s M. Ant��n Aparicio 《International journal of molecular sciences》2012,13(10):12710-12733
Historically, cell-signaling pathways have been studied as the compilation of isolated elements into a unique cascade that transmits extracellular stimuli to the tumor cell nucleus. Today, growing evidence supports the fact that intracellular drivers of tumor progression do not flow in a single linear pathway, but disseminate into multiple intracellular pathways. An improved understanding of the complexity of cancer depends on the elucidation of the underlying regulatory networks at the cellular and intercellular levels and in their temporal dimension. The high complexity of the intracellular cascades causes the complete inhibition of the growth of one tumor cell to be very unlikely, except in cases in which the so-called “oncogene addiction” is known to be a clear trigger for tumor catastrophe, such as in the case of gastrointestinal stromal tumors or chronic myeloid leukemia. In other words, the separation and isolation of the driver from the passengers is required to improve accuracy in cancer treatment. This review will summarize the signaling pathway crossroads that govern renal cell carcinoma proliferation and the emerging understanding of how these pathways facilitate tumor escape. We outline the available evidence supporting the putative links between different signaling pathways and how they may influence tumor proliferation, differentiation, apoptosis, angiogenesis, metabolism and invasiveness. The conclusion is that tumor cells may generate their own crossroads/crosstalk among signaling pathways, thereby reducing their dependence on stimulation of their physiologic pathways. 相似文献