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61.
Summary Cationic polymerization of p-methoxystyrene initiated by HI/ZnI2 in toluene afforded living polymers not only at low temperature (–15°C) but at room temperature (+25°C) as well. The number-average molecular weight of the polymers was directly proportional to monomer conversion and in excellent agreement with the calculated value assuming that one polymer chain forms per unit hydrogen iodide. On addition of a fresh feed of monomer at the end of the first-stage polymerization, the added feed was smoothly polymerized at nearly the same rate as in the first stage; the polymer molecular weight further increased in direct proportion to monomer conversion and was close to the calculated value for living polymer. Throughout these reactions, the molecular weight distribution of the polymers stayed very narrow (¯Mw/¯Mn<1.1). This is the first example of living cationic polymerizations of styrene derivatives that proceed even at room temperature. 相似文献
62.
Saburo Komori Mitsuo Okahara Kenzo Okamoto 《Journal of the American Oil Chemists' Society》1960,37(10):468-473
Summary Since the long-chain fatty acid sucrose diesters inevitably produced in the synthesis of monoesters are only slightly soluble
in water, no important use can be found for them at the present time except as oilsoluble emulsifying agents.
In order to exploit new uses we have attempted to improve their solubility in water by introducing oxyethylene radicals into
the molecule.
The addition reaction of ethylene oxide with the sucrose diesters was carried out in an autoclave in the presence of alkaline
catalysts. With the reaction temperature maintained between 100–130° the pressure decreased as the reaction proceeded, and
one to two hours were required to consume the ethylene oxide used.
The addition products are yellow or orange oily materials soluble in water. Aqueous solutions showed good surface-active properties. 相似文献
63.
The present study was carried out to examine if the positional distribution of medium-chain fatty acid (MCF) in dietary synthetic
fat influences lymphatic transport of dietary fat and the chemical composition of chylomicrons in rats with permanent cannulation
of thoracic duct. Four types of synthetic triacylglycerol were prepared: (i) sn-1(3) MCF-sn 2 linoleic acid, (ii) interesterified sn-1(3) MCF-sn 2 linoleic acid, (iii) sn-2 MCF-sn-1(3) linoleic acid, and (iv) interesterified sn-2 MCF-sn-1(3) linoleic acid. A purified diet composed of equal amounts of the synthetic fat and cocoa butter was given to rats with
permanent lymph duct cannulation. The positional distribution of MCF in the dietary fat had no significant effect on the lymph
flow, triacylglycerol output, phospholipid output, lipid composition of chylomicrons, or the particle size. The positional
distribution of MCF in the synthetic triacylglycerol was maintained in the chylomicron triacylglycerol. These results showed
that MCF in the dietary triacylglycerol is transported into lymphatics and the positional distribution is well preserved in
chylomicron triacylglycerol. 相似文献
64.
Toyama Mitsutoshi; Yamashita Mitsuo; Yoneda Morihide; Zaborowski Andrzej; Nagato Masaki; Ono Hisayo; Hirayama Noriaki; Murooka Yoshikatsu 《Protein engineering, design & selection : PEDS》2002,15(6):477-483
Despite the structural similarities between cholesterol oxidasefrom Streptomyces and that from Brevibacterium, both enzymesexhibit different characteristics, such as catalytic activity,optimum pH and temperature. In attempts to define the molecularbasis of differences in catalytic activity or stability, substitutionsat six amino acid residues were introduced into cholesteroloxidase using site-directed mutagenesis of its gene. The aminoacid substitutions chosen were based on structural comparisonsof cholesterol oxidases from Streptomyces and Brevibacterium.Seven mutant enzymes were constructed with the following aminoacid substitutions: L117P, L119A, L119F, V145Q, Q286R, P357Nand S379T. All the mutant enzymes exhibited activity with theexception of that with the L117P mutation. The resulting V145Qmutant enzyme has low activities for all substrates examinedand the S379T mutant enzyme showed markedly altered substratespecificity compared with the wild-type enzyme. To evaluatethe role of V145 and S379 residues in the reaction, mutantswith two additional substitutions in V145 and four in S379 wereconstructed. The mutant enzymes created by the replacement ofV145 by Asp and Glu had much lower catalytic efficiency forcholesterol and pregnenolone as substrates than the wild-typeenzyme. From previous studies and this study, the V145 residueseems to be important for the stability and substrate bindingof the cholesterol oxidase. In contrast, the catalytic efficiencies(kcat/Km) of the S379T mutant enzyme for cholesterol and pregnenolonewere 1.8- and 6.0-fold higher, respectively, than those of thewild-type enzyme. The enhanced catalytic efficiency of the S379Tmutant enzyme for pregnenolone was due to a slightly high kcatvalue and a low Km value. These findings will provide severalideas for the design of more powerful enzymes that can be appliedto clinical determination of serum cholesterol levels and assterol probes. 相似文献
65.
Dimethylsiloxane-tetramethyl-p-silphenylenesiloxane-dimethylsiloxane (DMS-TMPS-DMS) triblock copolymer was synthesized by employing living anionic polymerization of hexamethylcyclotrisiloxane (D3). Two synthetic methods were carried out for the polymerization. One of those methods was the anionic polymerization of D3 initiated at the silanolate anion which was prepared from the terminal hydroxyl group of silanol-terminated TMPS prepolymer by reaction with n-butyllithium (method 1). The other was the coupling reaction of vinyl-terminated TMPS prepolymer with hydrosilyl-terminated DMS prepolymer obtained from the anionic polymerization of D3 by using diphenylmethylsilanolate anion as initiator (method 2). In method 1, DMS contents of the copolymers ranged from 25.8 to 72.5 wt% and the values agreed with the ratio of D3 to TMPS prepolymer. The weight-average molecular weights ranged from 1.36×104 to 19.4×104 and were close to the predicted values calculated from the of the TMPS prepolymer and the amount of D3 added. In the case of method 2, weight-average molecular weights ranged from 19.5×104 to 24.2×104. The high molecular weight copolymer could thus be obtained by method 2. Intrinsic viscosity values of the triblock copolymers agreed with calculated values obtained by considering the copolymer as a binary mixture of these homopolymers. Differential scanning calorimetry and thermogravimetry were carried out on the triblock copolymers. The equilibrium melting temperatures of each of the copolymers were very close to that of poly-TMPS (160°C). The glass transition temperature and heat of fusion were decreased as the DMS content was increased. The thermogravimetric curves for the copolymers indicated that the thermal stability of the triblock copolymer was intermediate between the DMS and TMPS homopolymers. 相似文献
66.
The characteristics of gas bubbles in a 5 cm diameter bubble column equipped with a single orifice of 1,3 or 5 mm diameter were investigated under system pressure of 0.1-15 MPa. The formation of gas bubbles was strongly affected by the system pressure. Under high pressures a dispersed gas jet was formed at gas velocities where spherical gas bubbles would have been formed at atmospheric pressure. The critical gas velocity between the bubbling regime and the jetting regime was correlated with the liquid phase Weber number and the gas phase Reynolds number based on the gas velocity at the orifice. Bubble size and gas holdup in the main part of the bubble column were also affected by the bubble formation pattern at the distributor 相似文献
67.
Summary Several metal oxides-supported TiCl3 catalysts were prepared and propylene polymerization was conducted over them without cocatalysts. It was found that isotactic polymerization of propylene took place effectively over them. 相似文献
68.
Summary It was found that isotactic polymerization of propylene took place over titanium ion-exchanged Y-zeolite without organometallic compounds. The results obtained have led to the conclusions that Ti4+ species as well as Ti3+ species are active for the polymerization and that neither Ti-alkyl bonds nor Cl ligands are necessarily essential for polymerization of propylene. 相似文献
69.
For the elucidation of the crystal structures of the two crystalline allomorphs of cellulose triacetate (CTA), namely CTA I and CTA II, two-dimensional (2D) solid-state through-bond 13C-13C and 1H-13C correlations NMR techniques applied to the two crystalline allomorphs of CTA. As a result, the 13C and 1H chemical shifts of the glucopyranose ring of CTA I and CTA II were completely assigned by the 2D NMR spectra of these allomorphs. On the 2D 13C-13C correlation spectrum of CTA II, two sets of the 13C-13C correlations from C1 to C6 were observed. This indicated that the CP/MAS 13C NMR spectrum of CTA II can be characterized by its overlapping of the 13C subspectra of two kinds of 2,3,6-triacetyl-anhydroglucopyranose units and that there are two magnetically non-equivalent sites in the unit cell of CTA II. In the case of CTA I, the numbers of respective 13C and 1H shifts of CTA I agreed with the those of the glucopyranose residue in the allomorph, strongly suggesting that the asymmetric unit of CTA I is only one glucose residue. In addition, conformational differences in the exocyclic C5-C6 bonds between CTA I and CTA II were strongly suggested by the notable differences in the 1H and 13C chemical shifts at the C6 sites of these allomorphs. 相似文献
70.
Fumiaki Kobayashi Toru Ogawa Mitsuo Akabori Yoshio Kato 《Journal of the American Ceramic Society》1995,78(8):2279-2281
Uranium-plutonium nitride is a candidate fuel for fast reactors, but its major drawback is 14 C formation from natural nitrogen. One would probably have to use highly 15 N-enriched nitrogen. A pyrochemical process with molten-salt electroreflning has been proposed as a means to increase the nuclear proliferation resistance of the fuel cycle. Molten-salt electroreflning could also be applied to nitride fuels to make possible the recycling of 15 N. The anodic dissolution behavior of UN in LiCI-KCI melt was studied to provide the basis for a feasibility study of electroreflning of irradiated nitride fuels. 相似文献