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991.
PurposeThe use of a magnetic nanoparticle tracer and handheld magnetometer for sentinel lymph node biopsy (SLNB) was recently introduced to overcome drawbacks associated with the use of radioisotope tracers. Unlike the gamma probe, the used magnetometers are not only sensitive to the tracer, but also the diamagnetic human body. This potentially limits the performance of the magnetometer when used clinically.MethodsA phantom, mimicking the magnetic and mechanical properties of the human axilla, was constructed. The depth performance of two current generation magnetometers was evaluated in this phantom. LN-phantoms with tracer uptake ranging from 5 to 500 μg iron were placed at clinically relevant depths of 2.5, 4 and 5.5 cm. Distance-response curves were obtained to quantify the depth performance of the probes.ResultsThe depth performance of both probes was limited. In the absence of diamagnetic material and forces on the probe (ideal conditions) a LN-phantom with high uptake (500 μg iron) could first be detected at 3.75 cm distance. In the phantom, only superficially placed LNs (2.5 cm) with high uptake (500 μg iron) could be detected from the surface. The penetration depth was insufficient to detect LNs with lower uptake, or which were located deeper.ConclusionThe detection distance of the current generation magnetometers is limited, and does not meet the demands formulated by the European Association for Nuclear Medicine for successful transcutaneous SLN localization. Future clinical trials should evaluate whether the limited depth sensitivity is of influence to the clinical outcome of the SLNB procedure. 相似文献
992.
Lars Wommer Winda Soerjawinata Roland Ulber Percy Kampeis 《Engineering in Life Science》2021,21(10):558
Purification of mRNA with oligo(dT)‐functionalized magnetic particles involves a series of magnetic separations for buffer exchange and washing. Magnetic particles interact and agglomerate with each other when a magnetic field is applied, which can result in a decreased total surface area and thus a decreased yield of mRNA. In addition, agglomeration may also be caused by mRNA loading on the magnetic particles. Therefore, it is of interest how the individual steps of magnetic separation and subsequent redispersion in the buffers used affect the particle size distribution. The lysis/binding buffer is the most important buffer for the separation of mRNA from the multicomponent suspension of cell lysate. Therefore, monodisperse magnetic particles loaded with mRNA were dispersed in the lysis/binding buffer and in the reference system deionized water, and the particle size distributions were measured. A concentration‐dependent agglomeration tendency was observed in deionized water. In contrast, no significant agglomeration was detected in the lysis/binding buffer. With regard to magnetic particle recycling, the influence of different storage and drying processes on particle size distribution was investigated. Agglomeration occurred in all process alternatives. For de‐agglomeration, ultrasonic treatment was examined. It represents a suitable method for reproducible restoration of the original particle size distribution. 相似文献
993.
磁共振波谱(magnetic resonance spectroscopy,MRS)技术的出现使活体检测组织的代谢和生化信息成为可能,随着其技术的不断成熟,其在临床的应用范围日益扩大。脑胶质瘤具有与正常脑组织不同的代谢特征,借助MRS技术一方面可以反映其代谢特征,另外可将其与正常脑组织区分,因此MRS技术特别是^1H-MRS在脑胶质瘤的诊断、鉴别诊断、分级及预后评估中应用日益广泛。本文就相关进展进行综述。 相似文献
994.
995.
S. Aime Monica Chiaussa Giuseppe Digilio Eliana Gianolio Enzo Terreno 《Journal of biological inorganic chemistry》1999,4(6):766-774
N,N′,N″,N‴ -pentaacetic acid) bearing different substituents for binding to human serum albumin (HSA) are compared. In spite of the structural
differences of the recognition synthon and of the residual electric charge, the two chelates display an analogous binding
affinity for the serum protein. Upon formation of the adducts with HSA, the exchange rates of the coordinated water appear
slowed down by an amount corresponding to ca. 50% of the rates found for the free complexes. The relaxivity of [Gd(BOM)3DTPA (H2O)]2 − is significantly higher than that of MS-325 either in the free complex or in the macromolecular adduct. Finally, the effect
of pH on the stability of the HSA adducts and on the values of their relaxivities has been investigated.
Received: 11 June 1999 / Accepted: 15 September 1999 相似文献
996.
Sonja Kazmer Keh-Ming Pan Lyubomir Vassilev 《Journal of biochemical and biophysical methods》1999,40(3):5537-117
An improved telomerase assay was developed that allows direct quantification of the enzyme activity by scintillation counting of the labeled telomerase product. The assay measures the incorporation of 32P-dGTP into telomeric repeats synthesized at the 3′ end of a biotinylated primer. Telomerase reaction product is separated from the reaction mix by streptavidin-coated magnetic beads and counted. The assay can be used for quantitative studies of human telomerase and its inhibitors. 相似文献
997.
Joshua Telser Hong-In Lee Brian M. Hoffman 《Journal of biological inorganic chemistry》2000,5(3):369-380
3 S4]+, S=1/2, composed of three, antiferromagnetically coupled high-spin ferric ions) by continuous wave (CW) and pulsed EPR techniques:
Azotobacter vinelandii ferredoxin I, Desulfovibrio gigas ferredoxin II, and the 3Fe forms of Pyrococcus furiosus ferredoxin and aconitase. The 35 GHz (Q-band) CW EPR signals are simulated to yield experimental g tensors, which either had not been reported, or had been reported only at X-band microwave frequency. Pulsed X- and Q-band
EPR techniques are used to determine electron spin-lattice (T
1, longitudinal) relaxation times at several positions on the samples' EPR envelope over the temperature range 2–4.2 K. The
T
1 values vary sharply across the EPR envelope, a reflection of the fact that the envelope results from a distribution in cluster
properties, as seen earlier as a distribution in g
3 values and in 57 Fe hyperfine interactions, as detected by electron nuclear double resonance spectroscopy. The temperature dependence of 1/T
1 is analyzed in terms of the Orbach mechanism, with relaxation dominated by resonant two-phonon transitions to a doublet excited
state at ∼20 cm−1 above the doublet ground state for all four of these 3Fe proteins. The experimental EPR data are combined with previously
reported 57Fe hyperfine data to determine electronic spin exchange-coupling within the clusters, following the model of Kent et al. Their model defines the coupling parameters as follows: J
13=J, J
12=J(1+ε′), J
23=J(1+ε), where J
ij
is the isotropic exchange coupling between ferric ions i and j, and ε and ε′ are measures of coupling inequivalence. We have extended their theory to include the effects of ε′≠0 and thus derived an exact expression for the energy of the doublet excited state for any ε, ε′. This excited state energy corresponds roughly to ε
J and is in the range 5–10 cm−1 for each of these four 3Fe proteins. This magnitude of the product ε
J, determined by our time-domain relaxation studies in the temperature range 2–4 K, is the same as that obtained from three
other distinct types of study: CW EPR studies of spin relaxation in the range 5.5–50 K, NMR studies in the range 293–303 K,
and static susceptibility measurements in the range 1.8–200 K. We suggest that an apparent disagreement as to the individual
values of J and ε be resolved in favor of the values obtained by susceptibility and NMR (J≳200 cm−1 and ε≳0.02 cm−1 ), as opposed to a smaller J and larger ε as suggested in CW EPR studies. However, we note that this resolution casts doubt on the accepted theoretical model for describing
the distribution in magnetic properties of 3Fe clusters.
Received: 23 December 1999 / Accepted: 8 March 2000 相似文献
998.
昆虫通过细胞免疫和体液免疫的协同作用对入侵的异物做出防御反应。在不同时间向棉铃虫体内注射亲水性硅珠后,测定了血浆中酚氧化酶(PO)的活性,同时研究了不同抑制剂和激活剂对注射硅珠后的酚氧化酶活性的影响。结果表明,注射亲水性硅珠后,棉铃虫血浆中酚氧化酶的活性明显升高。分别以牛胰蛋白酶和昆布多糖作为酚氧化酶原(proPO)的激活剂,发现两者都可激活注射硅珠后血浆中的proPO。以牛胰蛋白酶激活时,随着注射硅珠后时间的延长,PO活性逐渐增高;而用昆布多糖激活后PO活性也明显升高,但注射硅珠后不同时间proPO被昆布多糖激活的情况基本相似。这些结果表明,在异物入侵后酚氧化酶原有很大程度的积累,并能被激活,协同细胞免疫抵御异物入侵。P-NPGB和PTU几乎能完全抑制酚氧化酶的活性。 相似文献
999.
Isadora A. Oliveira Arlan S. Gon?alves Jorge L. Neves Mark von Itzstein Adriane R. Todeschini 《The Journal of biological chemistry》2014,289(1):423-436
Trypanosoma cruzi trans-sialidase (TcTS) is a key target protein for Chagas disease chemotherapy. In this study, we investigated the implications of active site flexibility on the biochemical mechanism of TcTS. Molecular dynamics studies revealed remarkable plasticity in the TcTS catalytic site, demonstrating, for the first time, how donor substrate engagement with the enzyme induces an acceptor binding site in the catalytic pocket that was not previously captured in crystal structures. Furthermore, NMR data showed cooperative binding between donor and acceptor substrates, supporting theoretical results. In summary, our data put forward a coherent dynamic framework to understand how a glycosidase evolved its highly efficient trans-glycosidase activity. 相似文献
1000.
Gliclazide is a second generation of hypoglycemic sulfonylurea and acts selectively on pancreatic β cell to control diabetes
mellitus. The objective of this study was to produce a controlled release system of gliclazide using chitosan beads. Chitosan
beads were produced by dispersion technique using tripolyphosphate (TPP) as gelating agent. The effects of process variables
including chitosan molecular weight, concentration of chitosan and TPP, pH of TPP, and cross-linking time after addition of
chitosan were evaluated by Taguchi design on the rate of drug release, mean release time (MRT), release efficiency (RE8%), and particle size of the beads. The blood glucose lowering effect of the beads was studied in normal and streptozotocin-diabetic
rats. The optimized formulation CL2T5P2t10 with about 31% drug loading, 2.4 h MRT, and 69.16% RE8% decreased blood glucose level in normal rats for 24 h compared to pure powder of gliclazide that lasted for just 10 h. 相似文献