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排序方式: 共有1027条查询结果,搜索用时 15 毫秒
1.
Rupam Sarma 《Inorganica chimica acta》2009,362(6):1681-55
The coordination polymerization from lead(II) nitrate on reaction with 4-nitrobenzoic acid and pyridine N-oxide at room temperature passes through stepwise ligand substitution reaction. An intermediate polymer [Pb(NB)(PyO)2(NO3)]n (where NB = 4-nitrobenzoate, PyO = Pyridine N-oxide) is formed to give the final polymer [Pb(NB)2(PyO)]n. A hydrated mononuclear complex [Pb(NB)2(PyO)(H2O)] is also formed if rigorous anhydrous condition is not maintained. The reaction is extended to 4,4′-bipyridyl N-oxide (BPNO), which initially gives a coordination polymer [Pb2(NO3)(NB)3(BPNO)2]n which gets converted to another coordination polymer [Pb(NB)2(BPNO)2]n. All these complexes are structurally characterized. 相似文献
2.
A series of metal carboxylates containing pyridine N-oxide are prepared via one pot synthesis and solid phase synthesis. The structural variations from metal to metal are observed. In the case of reactions of manganese(II) acetate with pyridine N-oxide in the presence of aromatic carboxylic acids, polymeric complexes with bridging aromatic carboxylate as well as bridging pyridine N-oxide are observed. Whereas, the reaction of copper(II) acetate with pyridine N-oxide in the presence of an aromatic carboxylic acid led to mononuclear or binuclear paddle wheel carboxylate complexes with monodentate pyridine N-oxide. Co-crystal of two neutral complexes having composition [Cu2(OBz)4(MeOH)2][Cu2(OBz)4(pyO)2] (where OBz = benzoate, pyO = pyridine N-oxide) each neutral parts have paddle wheel structure. Solid phase reaction of zinc chloride with sodium benzoate prepared in situ and pyridine N-oxide leads to a tetra-nuclear zinc complex. 相似文献
3.
Prasert Akkaramongkolporn Tanasait Ngawhirunpat Praneet Opanasopit 《AAPS PharmSciTech》2009,10(2):641-648
The differently sulfonated styrene–divinylbenzene cross-linked copolymer cationic exchange resins were prepared by oil-in-water
polymerization and varied degrees of sulfonation. Several characteristics of the obtained resins were evaluated, i.e., Fourier
transform infrared spectra, the ion-exchange capacity, microscopic morphology, size, and swelling. The resin characteristics
were altered in relation to the degree of sulfonation, proving that differently sulfonated resins could be prepared. The behavior
of chlorpheniramine (CPM) loading and in vitro release in the USP simulated gastric (SGF) and intestinal fluids (SIF) of the obtained resins were also evaluated. The CPM
loaded in the resinates (drug-loaded resins) increased with the increasing degree of sulfonic group and hence the drug binding
site in the employed resins. The CPM release was lower from the resins with the higher degree of sulfonic group due to the
increase in the diffusive path depth. The CPM release was obviously lower in SGF than SIF because CPM, a weak base drug, ionized
to a greater extent in SGF and then preferred binding with rather than releasing from the resins. In conclusion, the differently
sulfonated resins could be utilized as novel carriers for drug delivery. 相似文献
4.
This study aimed to prepare a novel quartz crystal microbalance (QCM) sensor for the detection of pirimicarb. Pirimicarb‐imprinted poly (ethylene glycol dimethacrylate‐N‐metacryloyl‐(l )‐tryptophan methyl ester) [p (EGDMA‐MATrp)] nanofilm (MIP) on the gold surface of a QCM chip was synthesized using the molecular imprinting technique. A nonimprinted p (EGDMA‐MATrp) nanofilm (NIP) was also synthesized using the same experimental technique. The MIP and NIP nanofilms were characterized via Fourier transform infrared spectroscopy attenuated total reflectance spectroscopy, contact angle, atomic force microscopy, and an ellipsometer. A competitive adsorption experiment on the sensor was performed to display the selectivity of the nanofilm. An analysis of the QCM sensor showed that the MIP nanofilm exhibited high sensitivity and selectivity for pirimicarb determination. A liquid chromatography‐tandem mass spectrometry method was prepared and validated to determine the accuracy and precision of the QCM sensor. The accuracy and precision of both methods were determined by a comparison of six replicates at three different concentrations to tomato samples extracted by using a Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method. The limit of detection of the QCM sensor was found to be 0.028 nM. In conclusion, the QCM sensor showed good accuracy, with recovery percentages between 91 and 94%. Also, the pirimicarb‐imprinted QCM sensor exhibited a fast response time, reusability, high selectivity and sensitivity, and a low limit of detection. Therefore, it offers a serious alternative to the traditional analytical methods for pesticide detection in both natural sources and aqueous solutions. 相似文献
5.
Dimitri Karamata Harold M. Pooley Michel Monod 《Molecular & general genetics : MGG》1987,207(1):73-81
Summary A localized region of low DNA sequence homology was revealed in two strains of Bacillus subtilis by a specific 100-fold reduction in transformation by W23 DNA of the tag1 locus, a teichoic acid marker of strain 168. Fifty nine rare recombinants, hybrid at this locus, had all acquired donor-specific phage resistance characters, while losing those specific to the 168 recipient. Chemical analysis of isolated cell walls showed that these modifications are associated with major changes in the wall teichoic acids. Genetic analysis demonstrated that determinants for the ribitol phosphate polymer of strain W23 had been transferred to 168, replacing those for the glycerol phosphate polymer in the recipient. All W23 genes coding for poly(ribitol phosphate) in the hybrids and those specifying anionic wall polymers in strain 168 are clustered near hisA. In addition to tag1, the region exchanged extends just beyond gtaA in some hybrids, whereas in others it may include the more distant gtaB marker, encompassing a region sufficient to contain at least 20 average-sized genes. Surface growth, flagellation, transformability and sporulation all appeared normal in hybrids examined. Recombinants without a major wall teichoic acid from either strain were not found, suggesting that an integral transfer of genes for poly(ribitol phosphate) from W23 had occurred in all hybrids isolated. We interpret these results as indicating an essential role for anionic wall polymers in the growth of B. subtillis. 相似文献
6.
Structures resembling Metallogenium spp. were observed in agar and in liquid cultures of a Mn-oxidizing basidiomycetous fungus only when Mn2+ was oxidized. Fungal viability was necessary for formation of the structures; Mn2+ concentration and the presence or absence of agar in the medium were important factors determining their morphology. Slide cultures revealed no identifiable cells in any stage of development. Fluorescent dyes that stained nucleic acids and polysaccharides in the fungal hyphae did not stain the Metallogenium-like structures. Likewise, Rhodamine 123, a fluorescent probe for membrane potential, stained fungal mitochondria, but did not stain the structures. Thin sections through the structures showed no biological membranes or other cellular features. Only the characteristic ultrastructure of biological Mn oxides were observed in serial thin sections. In agar, unfixed structures disappeared permanently during reduction of Mn oxides with hydroxylamine. Glutaraldehyde fixation stabilized these structures. Fixed structures lost most of their original phase density during reduction with hydroxylamine, but continuous microscopic observations showed that their phase density could be restored by staining with Coomassie blue. Structures that formed in liquid medium did not require stabilization with glutaraldehyde during reduction of Mn oxides. They, too, lost their original phase density during reduction with hydroxylamine; phase density could be restored by staining with cationic colloidal iron or Coomassie blue. The results suggest that the Metallogenium-like structures were formed as a result of Mn oxidation associated with exopolymers produced by the fungus.Non-standard abbreviations HEPES
(N-hydroxyethylpiperazine-N-2-ethane sulfonic acid)
- DAPI
(4,6-diamidino-2-phenylindole)
- PIPES
(piperazine-N,N-bis[2-ethane sulfonic acid]) 相似文献
7.
A comparative study on tyrosine oxidation was made with a pure cationic and anionic peroxidase from peanut cell culture medium. The results showed that both isozymes possessed almost identical capacity to oxidize tyrosine to dityrosine, isodityrosine and polytyrosine with the main difference being the pH optimum (pH 4 for the anionic and pH 7 for the cationic isozyme). Variation of reaction time after 1.5 h incubation had little effect on the quantity and quality of the oxidation products. On the other hand, increase of enzyme units correspondingly increased tyrosine-oxidation. The removal of heme and carbohydrate moieties from the holoenzyme arrested the reaction thereby suggesting the role played by these moieties in stabilizing the active site of peroxidase isoenzymes. Isolated cell wall extracts catalyzed the tyrosine-oxidation equally well as the purified peroxidase. Even though polyclonal antibodies against anionic peroxidase inhibited the in vitro tyrosine reaction they did not affect the tyrosine oxidation by the cell walls, while the cationic antibodies did.Abbreviations A.PRX
anionic peanut peroxidase
- C.PRX
cationic peanut peroxidase
- PcAb
polyclonal antibodies
- ELISA
enzyme-linked-immuno-sorbent-assay
- TFMS
trifluoromethane sulfonic acid 相似文献
8.
Dissolved nutrient inputs in bulk precipitation and outputs in streamwater were measured during 3 years of contrasting hydrological conditions in a 6.3-ha, grazed heathland watershed on schists in the Montseny mountains (NE Spain), drained by an intermittent stream. On average, 39% of the precipitation became streamflow. Bulk precipitation delivered positive net alkalinity (mean 0.22 keq/ha/yr), sulphate input was moderate (9.0 kg SO4-S/ha/yr), and the mean input of inorganic N was not exceptionally high (6.6 kg/ha/yr). Ion concentrations were relatively low in streamwater; SO4
2- was the dominant anion. Most concentrations in streamwater varied seasonally, with maxima in late summer or early autumn and minima in spring. This pattern probably resulted from increased availability of ions for leaching due to decomposition of organic matter and chemical weathering during the warm period. Nitrate concentrations were relatively high in winter and dropped sharply in early spring, probably because of biological uptake. Annual element outputs in streamwater varied between years and seemed to be controlled by both the amount of annual streamflow and its seasonal distribution. Annual inputs exceeded outputs for dissolved inorganic N. The watershed accumulated H+ and Ca2+, had net losses of Na+ and Mg2+, and was close to steady state for K+, SO4
2-, Cl- and alkalinity. The chloride budgets gave no evidence of substantial dry deposition in this system. The cationic denudation rate was negative (-0.14 keq/ha/yr) because Ca2+ retention was higher than net exports of Na+ and Mg2+ from silicate weathering. Low nutrient export and little production of alkalinity suggest that this watershed has a low buffering capacity. 相似文献
9.
Human erythrocytes were incubated in isotonic solutions of different monovalent cations. The apparent size of the red cells
measured on scanning electron microscopic pictures decreases in the order Li+>Na+=K+>Rb+. These differences in size are abolished after pretreatment with trypsin, which removes a large part of the charges associated
with membrane glycoproteins. Shape alterations are also observed. Normal biconcave shapes are visible after Na+ or K+ incubation, whereas Li+ leads to flabby, flattened cells with a certain tendency to crenation, and Rb+ causes more pronounced biconcavity with a certain tendency to cupping. The overall effects of pretreatment with trypsin are
similar to those of Li+. Our results provide evidence that the electrostatic repulsion of glycoproteins and other charged membrane components may
play an essential role in maintaining red cell shape. 相似文献
10.
Sheri L. Holmen Matt W. Vanbrocklin Robert R. Eversole Susan R. Stapleton Leonard C. Ginsberg 《In vitro cellular & developmental biology. Animal》1995,31(5):347-351
Cationic lipids are an effective means for transfecting nucleic acids into a variety of cell types. Very few of these lipids,
however, have been reported to be effective with primary cells. We report on the efficacy of several commercially available
cationic lipid reagents to transfect plasmid DNA into primary rat hepatocytes in culture. The reagents tested in this study
include TransfectAce, LipofectAmine, Lipofectin, N-[1-(2,3-dioleyloxy)propyl]-n,n,n-trimethylammoniumchloride (DOTMA), (N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethyl-ammonium
methylsulfate (DOTAP), and cetyltrimethyl-ammonium bromide/dioleoylphosphatidylethanol-amine (CTAB/DOPE). Electron micrographic
(EM) studies indicate that similar size Lipofectin and DOTAP vesicles contain DNA-like material internally and that these
vesicles attach to the cell membrane. DOTAP vesicles are multilamellar, appear as clusters, and have a high DNA-to-lipid ratio.
Lipofectin vesicles appear to attach to the cell surface as individual vesicles. The EM observations are consistent with current
theories on the mechanism of transfection by cationic lipids. While Lipofectin has proven to be effective in transfection
studies of primary cells in culture, we have found DOTAP to be a viable alternative. DOTAP yields transfection rates in hepatocytes
comparable to DOTMA and Lipofectin, however, at lower concentrations of reagent and at considerably less cost. Optimal conditions
for transfecting 5 μg of plasmid DNA with DOTAP were achieved by utilizing multilamellar (vortexed) vesicles at a concentration
of 15 μg DOTAP per 2 ml media in 60-mm plates for 2 h transfection time. In this study, DOTAP has proven to be economical,
easy to prepare, and very effective in transfecting DNA into primary rat hepatocytes. 相似文献