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21.
Latent low-coordinate titanium imides supported by a sterically encumbering beta-diketiminate ligand
Basuli F Clark RL Bailey BC Brown D Huffman JC Mindiola DJ 《Chemical communications (Cambridge, England)》2005,(17):2250-2252
Addition of an equal molar quantity of R- (R = Me, SiMe3) to complex (Nacnac)Ti=NAr(OTf) (Nacnac- =[ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3) forms the imido alkyl (Nacnac)Ti=NAr(R), which can be readily protonated to afford [(Nacnac)Ti=NAr(L)]+ (L = THF, Et2O, eta1-C6H5NMe2), or treated with B(C6F5)3 to afford the zwitterion (Nacnac)Ti=NAr(micro-CH3)B(C6F5)3. 相似文献
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Doug Wingard 《Journal of Thermal Analysis and Calorimetry》2010,102(2):469-476
The Advanced Crew Escape Suit (ACES) is a pressurized suit worn by astronauts during launch and landing phases of Space Shuttle
operations. In 2008, a large tear (12.7–25.4 mm long, between the pinky and ring finger) in the ACES left-hand glove made
of neoprene latex rubber was found during training for Shuttle flight STS-124. An investigation to help determine the cause(s)
of the glove tear was headed by the NASA Johnson Space Center (JSC) in Houston, Texas. Efforts at JSC to reproduce the actual
glove tear pattern by cutting/tearing or rupturing were unsuccessful. Chemical and material property data from JSC such as
GC-MS, FTIR, DSC, and TGA mostly showed little differences between samples from the torn and control gloves. One possible
cause for the glove tear could be a wedding ring/band worn by an astronaut. Even with a smooth edge, such a ring could scratch
the material and initiate the tear observed in the left-hand glove. A decision was later made by JSC to not allow the wearing
of such a ring during training or actual flight. Another possible cause for the ACES glove tear is crystallinity induced by
strain in the neoprene rubber over a long period of time and use. Neoprene is one among several elastomers known to be susceptible
to crystallization, and such a process is accelerated with exposure of the material to cold temperatures plus strain. When
the temperature is lowered below room temperature, researchers have shown that neoprene crystallization may be maintained
at temperatures as high as 7.2–10 °C, with a maximum crystallization rate near −6.7 to −3.9 °C (Kell et al. J Appl Polym Sci
2(4):8–13, 1959 [1]). A convenient conditioning temperature for inducing neoprene crystallization is a typical freezer that is held near −17.8
°C. For work at the NASA Marshall Space Flight Center (MSFC), samples were cut from several areas/locations (pinky/ring finger
crotch, index finger and palm) on each of two pairs of unstrained ACES gloves for DSC and DMA thermal analysis testing. The
samples were conditioned in a freezer for various times up to about 14 days. Some rectangular conditioned samples were unstrained,
while most were subjected to strains up to 250% with the aid of two slotted aluminum blocks and two aluminum clamps per sample.
Trends were observed to correlate DSC data (heat of fusion) and DMA data (linear CTE and stress for iso-strain testing) with
(a) sample location on each glove; and (b) percent strain during conditioning. Control samples cut “as is” from each glove
location were also tested by DSC and DMA. 相似文献
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Two analytical procedures used to determine total, soluble, and insoluble solids in tomato paste were evaluated. The microwave oven (MO) method was compared to the vacuum oven (VO) method. The VO method is tedious and measured the three solids fractions in the paste directly, while the MO method measured the total solids directly but used an equation to calculate the water-soluble and -insoluble solids. The MO method was faster and less labor-intensive, and yielded small but statistically significant higher values for total and insoluble solids and lower statistically significant values for soluble solids. 相似文献
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Doug Hensley 《Mathematische Nachrichten》1997,184(1):177-190
Given a finite field Fq of order q, a fixed polynomial g in –Fq[X] of positive degree, and two elements u and v in the ring of polynomials in R = Fq [X]/gFq[X], the question arises: How many pairs (a, 6) are there in R × R so that ab ? 1 mod g and so that a is close to u while b is close to v ? The answer is, about as many as one would expect. That is, there are no favored regions in R × R where inverse pairs cluster. The error term is quite sharp in most cases, being comparable to what would happen with random distribution of pairs. The proof uses Kloosterman sums and counting arguments. The exceptional cases involve fields of characteristic 2 and composite values of g. Even then the error term obtained is nontrivial. There is no computational evidence that inverses are in fact less evenly distributed in this case, however. 相似文献
29.
The electron affinity and first three ionization potentials of C3 are calculated using the multiconfigurational SCF and configuration interaction methods and by Möller-Plesset perturbation theory. Whereas Koopmans' theorem and SCF calculations indicate that the first cation state is 2Πu, upon inclusion of correlation effects both the 2Σu and 2Σg cation states are found to lie lower in energy. CI calculations indicate that the ground state (2Πg) anion is stable by 1.74 eV. Allowing for the error in the calculated electron affinity of the carbon atom, C3? is estimated to be stable by 2.0 eV, in excellent agreement with the 2.05 eV value determined from recent photodetachment measurements. No excited anion states are found to be bound at the equilibrium geometry of the neutral molecule. 相似文献
30.
Using the finite dimensional example of
, the universal covering of PSU(1,1), as a guide, we revisit the orbit method as it applies to
, the universal central extension of
. We clarify some aspects of the classification of coadjoint orbits, determine boundedness properties of the natural height function on these orbits, and calculate orbital integrals. 相似文献