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111.
A double hydrogen bonding (DHB) hydrogel is constructed by copolymerization of 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine (hydrophobic hydrogen bonding monomer) and N,N‐dimethylacrylamide (hydrophilic hydrogen bonding monomer) with polyethylene glycol diacrylates. The DHB hydrogels demonstrate tunable robust mechanical properties by varying the ratio of hydrogen bonding monomer or crosslinker. Importantly, because of synergistic energy dissipating mechanism of strong diaminotriazine (DAT) hydrogen bonding and weak amide hydrogen bonding, the DHB hydrogels exhibit high toughness (up to 2.32 kJ m−2), meanwhile maintaining 0.7 MPa tensile strength, 130% elongation at break, and 8.3 MPa compressive strength. Moreover, rehydration can help to recover the mechanical properties of the cyclic loaded–unloaded gels. Attractively, the DHB hydrogels are responsive to CO2 in water, and demonstrate unprecedented CO2‐triggered shape memory behavior owing to the reversible destruction and reconstruction of DAT hydrogen bonding upon passing and degassing CO2 without introducing external acid. The CO2 triggering mechanism may point out a new approach to fabricate shape memory hydrogels. 相似文献
112.
We consider the possibility of the analytic continuation of the Dirichlet series SP;Z(s) associated with a polynomial P(x) and auxiliary series Z(s). In fact, we derive a certain criterion for the analytic continuation for some class of polynomials and give examples such that SP;Z(s) cannot be continued meromorphically to the whole plane C. We also study the asymptotic behaviors of the sum MP(x)=∑P(n1,…,nk)?xΛ(n1)?Λ(nk) considered first by M. Peter. Generalizations of this sum are also considered. 相似文献
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To fully exploit the device potential of graphene, reliable production of large-area, high-quality samples is required. Epitaxial growth on metal substrates have shown promise in this regard, but further improvement would be facilitated by a more complete understanding of the atomistic processes involved in the early growth stages. Using first-principles calculations within density functional theory, we have investigated the energetics and kinetics of graphene nucleation and growth on a Cu(111) surface. Our calculations have revealed an energetic preference for the formation of stable one-dimensional carbon nanoarches consisting of 3-13 atoms when compared to two-dimensional compact islands of equal sizes. We also estimate the critical cluster size that marks the transition from nanoarch dominance to island dominance in the growth sequence. Our findings may provide the structural link between nucleated carbon dimers and larger carbon nanodomes, and are expected to stimulate future experimental efforts. 相似文献
116.
Surface states--the electronic states emerging as a solid material terminates at a surface--are usually vulnerable to contaminations and defects. The robust topological surface state(s) (TSS) on the three-dimensional topological insulators provide a perfect platform for exploiting surface states in less stringent environments. Employing first-principles density functional theory calculations, we demonstrate that the TSS can play a vital role in facilitating surface reactions by serving as an effective electron bath. We use CO oxidation on gold-covered Bi(2)Se(3) as a prototype example, and show that the robust TSS can significantly enhance the adsorption energy of both CO and O(2) molecules, by promoting different directions of static electron transfer. The concept of TSS as an electron bath may lead to new design principles beyond the conventional d-band theory of heterogeneous catalysis. 相似文献
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We present several new results involving Δ(x+U)?Δ(x), where U=o(x) and $$\varDelta(x):=\sum_{n\leq x}d(n)-x\log x-(2\gamma-1)x $$ is the error term in the classical Dirichlet divisor problem. 相似文献
119.
Wenguang Zhai 《Journal of Number Theory》2009,129(8):1820-1836
For a fixed prime q, let eq(n) denote the order of q in the prime factorization of n!. For two fixed integers m?2 and r with 0?r?m−1, let A(x;m,q,r) denote the numbers of positive integers n?x for which . In this paper we shall prove a sharp asymptotic formula of A(x;m,q,r). 相似文献
120.
具有五元环结构的偶氮化合物4,4-二甲基-4,5-二氢-3H-吡咯(N2C5H10),与Fe3(CO)12在甲苯中加热回流反应,生成双铁六羰基配合物Fe2(N2C5H10)(CO)6(1).反应中N=N双键被还原,配体以(N2C5H10)2-的形式与FeIFeI配位,形成具有蝶形结构的34e-化合物.研究了在脱羰基试剂Me3NO存在条件下,1和单齿膦配体PR3反应生成Fe2(N2C5H10)-(CO)5(PR3)(PR3=PPh3,2a;PCy3,2b)单取代配合物.光照条件下,化合物1中的CO配体还可以被双齿膦配体dppe[dppe=1,2-C2H4(PPh2)2]和dppbz[dppbz=1,2-C6H4(PPh2)2]取代,生成产物的类型和膦配体的夹角相关.与夹角较大的dppe反应,生成桥连产物Fe2(N2C5H10)(CO)4(μ-dppe)(3a);而与刚性较大的dppbz反应时,Fe2(NR)2的蝶形结构打开呈四元环;其中一个Fe上的CO被取代,dppbz与该Fe中心螯合,生成具有桥连CO的化合物Fe2(N2C5H10)(μ-CO)(CO)4(κ2-dppbz)(3b).合成具有FeI-CO-FeI结构的羰基化合物,一直是模拟[FeFe]氢化酶活性中心还原态结构Fe2(SR)2(μ-CO)-(CO)5-xLx的重要挑战.该类Fe2(NR)2(CO)6-x(PR3)x化合物的合成,能为探索模拟[FeFe]氢化酶活性中心结构提供新的途径和思路.以上化合物均通过核磁[31P(1H)NMR]、红外光谱(IR)、元素分析及X射线单晶结构衍射等表征. 相似文献